How to Prevent Formjacking on Ecommerce Sites: The Silent Threat Stealing Your Customers’ Data

If you run an online store, you’ve probably invested in secure payment gateways and SSL certificates to protect your customers. But there’s a growing cybersecurity threat that many ecommerce businesses overlook: formjacking. This sophisticated attack targets the forms on your website where customers enter their payment information, potentially compromising sensitive data without you or your customers noticing anything unusual.

According to Symantec’s Internet Security Threat Report, formjacking attacks affect an average of 4,800 websites each month, with small and medium-sized businesses being particularly vulnerable. For online retailers, this represents not just a data security issue but a serious threat to customer trust and business reputation.

What Is Formjacking and Why Is It Dangerous?

Formjacking occurs when cybercriminals inject malicious JavaScript code into the payment forms of ecommerce websites. This code silently captures credit card details and personal information as customers enter it, transmitting the data to hackers without disrupting the normal checkout process. What makes formjacking particularly insidious is that the transaction still completes successfully—neither the customer nor the merchant realizes that data has been stolen until fraudulent charges appear later.

The consequences of formjacking can be devastating for ecommerce businesses:

Financial losses from regulatory fines and potential lawsuits
Severe damage to brand reputation and customer trust
Potential liability for fraudulent charges and identity theft
Costs associated with forensic investigation and security remediation
Loss of compliance with payment card industry (PCI DSS) standards

According to the IBM Cost of a Data Breach Report, the average cost of a data breach for retail companies is $3.28 million. For small ecommerce businesses, such an incident can be existentially threatening.

How Formjacking Attacks Work: The Technical Breakdown

Understanding the mechanics of formjacking attacks is essential for implementing effective prevention strategies. These attacks typically follow a predictable pattern that targets vulnerabilities in your website’s code or third-party dependencies. Cybersecurity researchers at Trend Micro have documented that formjacking attacks have evolved from simple script injections to sophisticated operations that can evade standard security measures.

The typical formjacking attack follows these steps:

1. Identifying Vulnerabilities

Attackers first scan for security weaknesses in your ecommerce platform, looking for outdated software, insecure plugins, or vulnerable third-party services. They’re particularly interested in sites using older versions of popular ecommerce platforms like Magento, WooCommerce, or Shopify apps that haven’t been updated. According to OWASP (Open Web Application Security Project), injection flaws remain among the top web application security risks precisely because they enable attacks like formjacking.

2. Code Injection

Once a vulnerability is identified, hackers inject malicious JavaScript code into your website’s files. This code is specifically designed to target checkout forms where customers enter payment information. The injection might happen through:

Compromised third-party scripts (like analytics tools or chat widgets)
Supply chain attacks targeting your ecommerce platform
Exploitation of security vulnerabilities in plugins or extensions
Compromised admin credentials giving direct access to site files

3. Data Capture and Exfiltration

The injected code creates an invisible “listener” that captures form data as customers type it. This information is then transmitted to servers controlled by the attackers, often using encryption or obfuscation techniques to avoid detection by security systems. The sophisticated nature of modern formjacking means the data theft happens in real-time, before the information is even submitted or encrypted by your payment processor.

4. Normal Transaction Completion

What makes formjacking particularly effective is that after capturing the data, the malicious code allows the transaction to complete normally. The customer receives their order confirmation, the payment processes successfully, and neither party has any immediate indication that sensitive information has been compromised.

7 Essential Strategies to Prevent Formjacking Attacks

Protecting your ecommerce site from formjacking requires a multi-layered security approach that addresses vulnerabilities at different levels. The Cybersecurity and Infrastructure Security Agency (CISA) recommends implementing defense-in-depth strategies rather than relying on a single security measure. Here are seven critical steps every ecommerce business should take:

1. Implement Subresource Integrity (SRI) Checks

Subresource Integrity is a security feature that enables browsers to verify that resources they fetch (like JavaScript files) are delivered without unexpected manipulation. By adding integrity attributes to your script tags, you can ensure that browsers only execute scripts that match a cryptographic hash you’ve specified. This prevents modified or compromised scripts from running on your site.

To implement SRI, add an integrity attribute to your script tags like this:

<script src="https://example.com/script.js" integrity="sha384-oqVuAfXRKap7fdgcCY5uykM6+R9GqQ8K/uxy9rx7HNQlGYl1kPzQho1wx4JwY8wC" crossorigin="anonymous"></script>

This approach is particularly valuable for scripts loaded from third-party CDNs or external sources, which are common targets for formjacking attacks.

2. Deploy Content Security Policy (CSP) Headers

Content Security Policy is a powerful security layer that helps prevent cross-site scripting (XSS) and formjacking attacks by controlling which resources can be loaded and executed on your website. A properly configured CSP can block unauthorized scripts from running, even if they somehow make it onto your site.

A basic CSP header for an ecommerce site might look like this:

Content-Security-Policy: default-src 'self'; script-src 'self' https://trusted-analytics.com https://payment-processor.com; style-src 'self'; img-src 'self'; connect-src 'self';

This policy restricts scripts to load only from your domain and specified trusted sources. According to a study by Google, implementing CSP can reduce XSS risks by up to 95%, which directly impacts formjacking prevention since many attacks use similar injection techniques.

3. Use Client-Side JavaScript Security Tools

Several specialized security tools can detect and prevent formjacking by monitoring JavaScript behavior in real-time. Solutions like comprehensive cybersecurity platforms often include features that can detect suspicious script activities and block data exfiltration attempts.

These tools work by:

Monitoring DOM modifications that might indicate script injection
Detecting unauthorized access to form fields and input events
Identifying suspicious network requests that might be sending data to attackers
Alerting administrators to potential formjacking attempts in real-time

4. Implement Regular Security Scanning and Monitoring

Continuous security monitoring is essential for detecting formjacking attempts before they succeed. Regular scanning can identify malicious code injections and unauthorized changes to your website files. Several approaches should be combined:

File integrity monitoring: Tools that alert you when critical website files are modified
Vulnerability scanning: Regular automated checks for known security issues
Behavioral analysis: Systems that detect unusual patterns in how your website functions
Change detection: Services that notify you of unexpected changes to your website’s appearance or behavior

According to the Payment Card Industry Security Standards Council, implementing file integrity monitoring is a critical component of maintaining PCI DSS compliance for ecommerce businesses, directly addressing the risk of formjacking.

5. Secure Your Supply Chain

Many formjacking attacks target third-party scripts and services rather than your website directly. This “supply chain attack” approach exploits the trust relationship between your site and external resources. To mitigate this risk:

Carefully evaluate all third-party services before integrating them into your checkout process. Research from RiskIQ shows that 50-60% of formjacking attacks originate from compromised third-party services, making this a critical security consideration. Implement a vendor security assessment process that includes:

Reviewing the security practices and compliance certifications of service providers
Limiting third-party access to only what’s necessary for their function
Regularly auditing which external scripts are loading on your checkout pages
Considering the use of script-blocking technologies during sensitive transactions

6. Adopt Modern Payment Security Technologies

Modern payment technologies can significantly reduce the risk of formjacking by changing how payment data is handled on your website. Consider implementing:

Hosted Payment Pages

Redirect customers to your payment processor’s secure environment for the actual transaction, removing sensitive data handling from your website entirely. This approach has been shown to reduce payment fraud by up to 70% according to a study by Cybersource.

Tokenization

Replace sensitive card data with non-sensitive tokens that can’t be used for fraudulent transactions even if intercepted. Major payment processors like Stripe and PayPal offer tokenization services that can be integrated with most ecommerce platforms.

iFrames for Payment Forms

Load payment forms within secure iFrames provided by your payment processor, isolating them from the rest of your website code. This creates a security boundary that makes it much harder for formjacking scripts to access payment data.

7. Keep Your Platform and Dependencies Updated

Perhaps the most fundamental but often overlooked security measure is keeping all software components of your ecommerce site updated. According to Sucuri’s Website Threat Research Report, 49% of hacked websites were running outdated software at the time of compromise. This applies to:

Your ecommerce platform core (Magento, WooCommerce, Shopify, etc.)
All plugins, extensions, and modules
Server software and operating systems
Content management systems
Third-party libraries and dependencies

Implement a regular update schedule and consider automating security patches when possible. For critical ecommerce sites, consider setting up a staging environment to test updates before applying them to your production site.

Detecting Formjacking: Warning Signs Your Site May Be Compromised

Even with preventive measures in place, it’s crucial to monitor for signs that your site may have been compromised by a formjacking attack. Early detection can significantly limit the damage. Security researchers at Malwarebytes have identified several warning signs that every ecommerce business should watch for:

Technical Indicators

Regular technical audits can reveal formjacking attacks before they cause significant damage. Implement monitoring that checks for these specific warning signs:

Unexpected JavaScript: New or modified JavaScript files, particularly those loading from unfamiliar domains
Code obfuscation: Heavily obfuscated or encoded JavaScript that’s difficult to read (legitimate code rarely needs heavy obfuscation)
Unusual network requests: Outbound data transmissions to unknown servers, especially during checkout processes
Modified checkout pages: Any unexpected changes to checkout page code, even minor ones
Strange browser behavior: Checkout forms that behave unusually, like cursor jumping or delayed input

Customer Feedback Indicators

Sometimes your customers will be the first to notice something wrong. Pay close attention to:

Reports of unauthorized transactions on cards used on your site
Increased customer complaints about payment issues
Multiple customers reporting fraud from cards only used on your website
Unusual patterns in transaction failures or abandonments

According to the Federal Trade Commission, businesses that detect breaches early and respond appropriately face significantly lower costs and legal consequences than those that fail to identify compromise quickly.

Responding to a Formjacking Attack: Your Emergency Action Plan

If you discover evidence of formjacking on your ecommerce site, rapid response is critical to minimize damage. The first 24-48 hours after discovery are crucial for containing the breach and protecting your customers. Security experts at Batten Cyber recommend having a response plan ready before an incident occurs, with clear steps for each phase of the response:

Immediate Containment Steps

Your first priority should be stopping the data leak and preventing further compromise. Take these immediate actions:

Take affected payment forms offline – Replace with a temporary maintenance message or alternative payment method while you investigate
Identify and remove malicious code – Work with security professionals to locate and eliminate the formjacking scripts
Scan for backdoors and persistent threats – Attackers often leave multiple entry points
Reset all administrative credentials – Change passwords and access tokens for all systems
Implement IP blocking – Block connections to any suspicious domains identified in the attack

Investigation and Documentation

Once the immediate threat is contained, conduct a thorough investigation to understand the scope and impact of the breach:

Determine when the attack began and which customers might be affected
Identify the attack vector—how did the formjacking code get injected?
Document all affected systems and data types
Preserve evidence for potential legal proceedings and insurance claims
Analyze logs to understand the full extent of data exfiltration

Notification and Disclosure

Most jurisdictions have legal requirements for data breach notification. Follow these guidelines:

Consult with legal counsel about disclosure obligations
Notify affected customers promptly with clear information
Contact relevant regulatory authorities as required by law
Inform payment processors and card networks about the breach
Consider offering identity theft protection services to affected customers

The Identity Theft Resource Center recommends providing specific, actionable advice to affected customers rather than vague notifications. Tell them exactly what information was compromised and what steps they should take to protect themselves.

Formjacking Prevention for Different Ecommerce Platforms

Different ecommerce platforms have unique security considerations and built-in protections against formjacking. Understanding the specific vulnerabilities and security features of your platform is essential for implementing effective protection.

Magento (Adobe Commerce) Security

Magento has been a frequent target for formjacking attacks due to its popularity and extensive codebase. If you’re running a Magento store, pay particular attention to these security measures:

Security Patches: Magento regularly releases security patches that must be applied promptly
Admin Path: Change the default admin URL path from /admin to a custom path
Two-Factor Authentication: Enable 2FA for all admin accounts
Magento Security Scan Tool: Use Adobe’s free security scanning service
Custom Admin Username: Avoid using “admin” as your administrator username

According to Adobe Security, Magento sites should also implement the built-in Content Security Policy features and consider using the Magento Security Suite extension for enhanced protection against code injection attacks.

WooCommerce and WordPress Security

WooCommerce sites face unique challenges because they run on WordPress, which has its own security considerations. For WordPress-based ecommerce:

Security Plugins: Implement reputable security plugins like Wordfence or Sucuri
WordPress Hardening: Follow the official WordPress security hardening guidelines
Plugin Management: Minimize plugins and only use those from reputable developers
Database Prefix: Change the default WordPress database prefix (wp_)
Payment Gateway Integration: Use hosted payment options when possible

The WordPress Security Team recommends implementing file change detection specifically for the wp-content/themes and wp-content/plugins directories, as these are common targets for code injection in WooCommerce sites.

Shopify Security Considerations

While Shopify handles much of the security infrastructure for merchants, there are still important steps store owners should take:

App Vetting: Only install apps from the official Shopify App Store after reviewing permissions
Custom Code Review: Carefully audit any custom code or theme modifications
Staff Account Security: Implement strict access controls and 2FA for all staff accounts
Shopify Payments: Consider using Shopify Payments to reduce third-party payment risks
Regular Theme Updates: Keep your theme updated to incorporate security improvements

Shopify’s security team notes that while their platform handles PCI compliance for payment processing, merchants are still responsible for securing custom code and third-party integrations that could introduce formjacking vulnerabilities.

The Future of Formjacking and Evolving Threats

As security measures improve, cybercriminals continue to evolve their tactics. Understanding emerging trends in formjacking can help you stay ahead of threats. Cybersecurity researchers at Symantec have identified several concerning developments in formjacking techniques:

Emerging Formjacking Techniques

Recent security research has identified several advanced formjacking methods that are becoming more common:

Polymorphic Code: Formjacking scripts that change their signature to evade detection
WebSocket Exfiltration: Using WebSocket connections instead of HTTP to avoid network monitoring
Client-Side Encryption Bypass: Sophisticated techniques to capture data before encryption
Supply Chain Poisoning: Targeting the developers of popular third-party services
Browser Extension Exploitation: Using compromised browser extensions to inject code

Preparing for Next-Generation Threats

To stay protected against evolving formjacking techniques, forward-thinking ecommerce businesses should consider these advanced security approaches:

Runtime Application Self-Protection (RASP): Technologies that monitor and block attacks from within the application itself
AI-Powered Behavior Analysis: Machine learning systems that can identify unusual script behaviors
Client-Side API Security: Tools specifically designed to protect JavaScript APIs from manipulation
Zero Trust Architecture: Assuming no component is secure and verifying everything
Web Application Firewalls with JavaScript Analysis: Advanced WAFs that can detect malicious JavaScript

According to Gartner research, by 2025, 40% of organizations will adopt these advanced client-side protection technologies, up from less than 10% today.

Conclusion: Building a Formjacking-Resistant Ecommerce Business

Protecting your ecommerce site from formjacking isn’t a one-time project but an ongoing commitment to security. The most successful ecommerce businesses make security an integral part of their operations rather than an afterthought. By implementing the strategies outlined in this guide, you can significantly reduce your risk of becoming a formjacking victim.

Remember that security is a layered approach—no single solution will protect you completely. The combination of technical controls, vigilant monitoring, and rapid response capabilities creates a robust defense against formjacking and other ecommerce threats.

For ecommerce businesses that lack in-house security expertise, working with specialized security partners can provide access to advanced protection technologies and expert guidance. Cybersecurity solutions designed specifically for online retailers can help implement many of the protections discussed in this article without requiring deep technical knowledge.

Key Takeaways for Ecommerce Security

Formjacking is a significant threat that targets the most sensitive data your customers share with you
Prevention requires a multi-layered approach combining technical controls and operational practices
Regular monitoring and testing are essential for early detection
Having an incident response plan ready before an attack occurs is critical
Security is an ongoing process that must evolve as threats change

Ready to protect your online store from formjacking and other cybersecurity threats? Explore our top-rated ecommerce security tools — personally vetted by experts and available through Batten Cyber’s trusted marketplace.