Malformed FileZilla FTP client versions 3.7.3 and 3.5.3 are malware versions of famous open source FTP clients. Malware authors use very powerful and inconspicuous method to steal FTP log in credentials in this case. Log in details are sent to attackers from the ongoing FTP connection only once. Malware doesn’t search bookmarks or send any other files or saved connections. The whole operation is very quick and quiet. The absence of any suspicious activity is the biggest danger for average users.”]
Source: https://blog.avast.com/2014/01/27/malformed-filezilla-ftp-client-with-login-stealer/