“We assume that the stolen FTP accounts are further abused for upload and spread of malware. The first suspicious signs are 'bogus download URLs', AVAST said, noting that the malcious FileZilla installers are typically hosted on hacked websites with fake content.

One version of the malware (version 3.5.3) was compiled in September 2012, indicating that these attackers have been running this attack campaign for some time. “Any attempt to update the application fails, which is most likely a protection to prevent overwriting of malware binaries,” AVAST said. One sign that users may be using the malicious version of FileZilla is if the software update feature is not functioning. Stolen login credentials are encoded using a custom base64 algorithm and then sent to the IP 144.76.120.243, a server hosted at “Server Block” in Germany.ĪVAST found 3 domains linked to the IP, all registered through, a domain registrar associated with malicious activities and masks registrant contact information and ignores requests to suspend domains, acccording to AVAST. Malware doesn’t search bookmarks or send any other files or saved connections.” “Log in details are sent to attackers from the ongoing FTP connection only once. “The whole operation is very quick and quiet,” AVAST noted in a blog post. The malicious FTP program is fully functional and maintains the look of the official version, and has no evidence of suspicious behavior such as entries in the system registry, communication or changes in application look and feel, AVAST cautioned.Īccording to the security firm, the interface of the malicious installer is nearly identical to the official version, with just a slight difference in the version of NullSoft installer, which the malware uses 2.46.3-Unicode, while the official installer uses v2.45-Unicode.

Researchers from AVAST are warning users to beware of modified and malicious versions of the popular open source FileZilla FTP client that captures login details and sends them to a server hosted in Germany.

Filezilla malware warning