Trend Micro InterScan VirusWall contains a flaw that may allow a remote attacker to bypass antivirus protection. The problem is that the program does not include support for HTTP/1.1 chunked transfer encoding. It is possible that the flaw may allow a remote attacker to send malicious files resulting in a loss of integrity.
Upgrade to version 5.0 or higher, as it has been reported to fix this vulnerability. An upgrade is required as there are no known workarounds.