FBI: Beware of Malware-Infested Online File Converter Tools

The FBI’s Denver Field Office has issued a warning about cybercriminals using free online file conversion tools to distribute malware, potentially leading to ransomware infections and identity theft.

Often advertised as simple converters for documents, images, or media files, these tools can secretly embed malicious software into the downloaded files.

File converter malware

According to the FBI, criminals are leveraging free file conversion and downloading tools to infect victims’ computers. These websites appear to offer legitimate services—such as converting a Word document to PDF, merging multiple image files, or downloading MP3 and MP4 files—but the output file may contain hidden malware. Once executed, this malware grants attackers unauthorized access to the victim’s system.

Beyond direct infections, these tools can also scrape sensitive data from uploaded documents, including:

• Personally identifiable information (Social Security numbers, birth dates, phone numbers)
• Banking credentials and financial data
• Cryptocurrency wallet details, including seed phrases
• Email addresses and passwords

Victims may not immediately realize their system has been compromised, only discovering the breach once they experience ransomware attacks or financial fraud.

Shady operations and ownership

Many of these free converter tools operate anonymously, making it difficult to verify their legitimacy. Unlike software from reputable developers, these services often lack transparency about their ownership, security policies, or data handling practices. Some may even impersonate well-known applications to appear credible or steal user-uploaded files to scrutinize them for sensitive data.

This type of threat is not new. In 2021, ESET Research identified an infostealer campaign that disguised itself as a popular application, including FreePdfConvert. Attackers used malicious ZIP files hosted on cloud storage services to target users in South America. The campaign relied on fake landing pages and malware-laden downloads, similar to the tactics used in the current scheme highlighted by the FBI.

To stay safe from this kind of threat, be very selective with what online tools you use and never upload sensitive files on any of them. In general, it is recommended to stick to reputable software providers rather than free, web-based converters. Finally, it is crucial to scan any downloaded file before opening it to check for malware.