Fake Online File Converters Deploying Ransomware

Security researchers have identified a growing trend of malicious file conversion websites being used as vectors for malware distribution and, in more severe cases, ransomware deployment. Following an FBI warning issued by their Denver field office, our research team has analyzed this emerging threat that targets users seeking convenient document conversion services online.

Threat Information

How the Fake File Converter Attack Works

This sophisticated scheme leverages the widespread need for quick file format conversions to lure unsuspecting victims. The attack progresses through several stages, creating multiple opportunities for cybercriminals to harvest sensitive information and deploy malicious payloads:

1. Initial Attraction: Cybercriminals create convincing websites that advertise free document conversion services, such as PDF to Word, merging PDF files, or other common file transformations
2. Website Positioning: These fraudulent sites are often promoted through search engine optimization techniques or even Google Ads, appearing prominently in search results for terms like “free PDF converter” or “online file merger”
3. Document Upload: When a user uploads a document for conversion, the malicious site actually processes it in two ways – performing the promised conversion (to appear legitimate) while simultaneously scraping the document for sensitive information
4. Malware Distribution: The site delivers a converted file that contains embedded malware, often disguised as a browser plugin, additional software, or part of the conversion process
5. Remote Access Establishment: Once executed, the malware establishes a connection to the attackers’ command and control servers, potentially granting them remote access to the victim’s device
6. Information Theft: In the background, attackers may exfiltrate sensitive data, monitor user activity, or steal credentials from browsers and password managers
7. Ransomware Deployment: In the most severe cases, the initial malware serves as a loader for ransomware that encrypts the victim’s files and demands payment for decryption

Specific Attack Scenarios

According to research from Malwarebytes, these malicious file converters typically employ one of these three main attack scenarios:

1. Direct Malware Download: The site persuades users to download a dedicated tool or application to perform the conversion, which is itself the malware
2. Malicious Browser Extensions: The site recommends installing a browser extension for easier future conversions. These extensions often function as browser hijackers and adware that can modify search results, display unwanted ads, or collect browsing data
3. Weaponized Output Files: In the most sophisticated approach, the seemingly legitimate converted file contains embedded malicious code that, when opened, downloads and installs information stealers or other malware. This means everyone who opens the converted file becomes infected

What makes these attacks particularly effective is that the conversion service actually works as advertised. Users get their converted files and may even recommend the service to colleagues or friends, unwittingly spreading the threat further.

Known Malicious Domains

Malwarebytes security researchers have identified and blocked numerous file converter domains involved in distributing malware. Below are some recently flagged examples and their associated threat classifications:

This list represents only a small fraction of malicious converter sites currently active. New domains are constantly being registered as older ones get flagged and blocked by security tools.

Red Flags and Warning Signs

Users should be vigilant and watch for these common indicators that a file conversion service may be malicious:

• Excessive permissions: The website requests unnecessary permissions or asks you to disable security features
• Installation requirements: The service claims you need to install special software or browser extensions to perform basic conversions
• Missing information: The website lacks proper contact information, privacy policies, or terms of service
• Too good to be true: The service offers premium features completely free while legitimate competitors charge for similar capabilities
• Suspicious URLs: The domain name contains random characters, misspellings, or unusual top-level domains
• Poor design or translations: The website contains obvious spelling errors, awkward phrasing, or unprofessional design elements
• Missing security indicators: The site lacks basic security features like HTTPS (secure connection) or displays security warnings in your browser

Types of Data at Risk

When users upload documents to these malicious services, attackers can extract various types of sensitive information:

• Personal identifiers: Names, addresses, phone numbers, Social Security/national ID numbers
• Financial information: Bank account details, credit card numbers, financial statements
• Credential data: Usernames, passwords, API keys embedded in documents
• Cryptocurrency information: Wallet addresses, seed phrases, private keys
• Business secrets: Intellectual property, confidential business plans, proprietary information
• Legal documents: Contracts, agreements, personal legal paperwork

Examples of Malware Delivered via Fake Converters

According to the FBI advisory and our research, these fraudulent services have been observed distributing various types of malware, including:

• Remote Access Trojans (RATs): Like Altruistic Trojan and others that give attackers complete control over the infected system
• Information Stealers: Malware designed to harvest passwords, browser cookies, cryptocurrency wallets, and other sensitive data
• Banking Trojans: Specialized malware like Zeus variants that target financial credentials and banking information
• Ransomware: In the most severe cases, these services have been linked to ransomware deployment, including emerging variants like QWCrypt
• Cryptominers: Hidden software that uses the victim’s computer resources to mine cryptocurrency for the attackers
• Browser Hijackers: Malware that modifies browser settings to display unwanted ads, redirect searches, and collect browsing data
• Potentially Unwanted Programs (PUPs): Software that bundles with the converter tool but performs unwanted actions like displaying ads or collecting data

Protection Strategies

To protect yourself from threats posed by fake file converters, consider implementing these security measures:

1. Use reputable services: Stick to well-known, established file conversion services with positive reviews and a history of trustworthy operation
2. Verify website legitimacy: Before uploading files, use website reputation tools like GridinSoft’s Website Reputation Checker to verify the site’s safety rating
3. Consider offline alternatives: Use built-in conversion features in software you already own, such as Microsoft Office or Adobe products
4. Check file safety after download: Scan any converted files with antivirus software before opening them
5. Be cautious with sensitive documents: Avoid uploading documents containing personal, financial, or confidential information to any online converter
6. Keep software updated: Ensure your operating system and applications have the latest security patches to prevent exploitation of known vulnerabilities
7. Use security software: Maintain comprehensive security protection with features like real-time scanning, web protection, and ransomware detection
8. Use browser protection: Install security-focused browser extensions that can block malicious websites and warn about potential threats

As FBI Denver Special Agent in Charge Mark Michalek states: “The best way to thwart these fraudsters is to educate people so they don’t fall victim to these fraudsters in the first place.”

What to Do If You’ve Used a Suspicious Converter

If you suspect you’ve already used a potentially malicious file conversion service, take these steps immediately:

1. Disconnect from the internet: Temporarily disconnect your device to prevent further data exfiltration or command reception
2. Run a comprehensive security scan: Use reputable security software to scan your entire system for malware
3. Change passwords: Update passwords for important accounts, especially if you shared documents containing credentials
4. Monitor financial accounts: Watch for unauthorized transactions and consider setting up alerts for suspicious activity
5. Check for unusual activity: Look for unexpected files, processes, or behavior on your device that might indicate compromise
6. Contact financial institutions: If you’ve shared financial information, contact your bank and credit card companies immediately to take protective measures
7. Report the incident: File a report with the Internet Crime Complaint Center (IC3) to help authorities track and combat these threats
8. Consider professional help: For businesses or severe cases, consult with cybersecurity professionals for proper incident response

Connection to Other Threats

This attack vector shares similarities with other cyber threats we’ve analyzed:

• FakeCaptcha URL Scam — Uses deceptive web interfaces to trick users into executing malicious code
• Clarity Tab Browser Hijacker — Exploits user trust to deliver unwanted software that modifies browser settings
• Chase Transfer Email Scam — Leverages legitimate-appearing services to trick users into sharing sensitive information

Real-World Cases

The FBI Denver field office has reported an increase in victims falling prey to these scams, resulting in significant financial and data losses. One notable case involved a small business that used what appeared to be a legitimate PDF merger tool to compile confidential financial documents. Within 48 hours, the company experienced a ransomware attack demanding $75,000 for decryption, alongside evidence that sensitive client information had been exfiltrated.

In another recent case, a research group uploaded scientific papers to a document converter to create a unified presentation. The malware deployed through the conversion service not only stole intellectual property but also established persistent access that remained undetected for months, allowing attackers to monitor communications and research progress.

Conclusion

Fake file converters represent a significant but often overlooked threat vector in today’s cybersecurity landscape. By exploiting the common need for quick document conversion services, cybercriminals create effective traps that can lead to data theft, financial losses, and even ransomware attacks.

The most effective defense is awareness combined with preventive measures. Being selective about which services you use, verifying website legitimacy before uploading sensitive documents, and maintaining robust security practices can significantly reduce your risk exposure to these threats.

As this threat continues to evolve, we’ll update our analysis and recommendations to help users stay protected against these deceptive tactics.