The AV engine before DAT 5600 in McAfee VirusScan, Total Protection, Internet Security, SecurityShield for Microsoft ISA Server, Security for Microsoft Sharepoint, Security for Email Servers, Email Gateway, and Active Virus Defense allows remote attackers to bypass virus detection via (1) an invalid Headflags field in a malformed RAR archive, (2) an invalid Packsize field in a malformed RAR archive, or (3) an invalid Filelength field in a malformed ZIP archive.