F-Secure Anti-Virus for Linux Gateways 4.65 allows remote attackers to cause a denial of service (possibly fatal scan error), and possibly bypass virus detection, by inserting invalid characters into base64 encoded content in a multipart/mixed MIME file, as demonstrated with the EICAR test file.
http://www.securityfocus.com/bid/21461
http://www.securityfocus.com/archive/1/453654/100/0/threaded