The criminals behind the malware delivery system for GameOver Zeus have a new trick. Encrypting their EXE file so that as it passes through your firewall, webfilters, network intrusion detection systems and any other defenses you may have in place, it is doing so as a non-executable “.ENC” file. Malcovery Security’s malware analyst Brendan Griffin let me know about this new behavior on January 27, 2014, and has seen it consistently since that time. The new detection rate for the Zeus downloads has consistently been ZERO of FIFTY at VirusTotal.”]
Source: http://garwarner.blogspot.com/2014/02/gameover-zeus-now-uses-encryption-to.html