Trojan.Packed is a heuristic detection for files that may have been obfuscated or encrypted in order to conceal files from antivirus software. A packer is a tool that compresses, encrypts or obfuscates Windows PE files. Malware authors often use packers to conceal threats from detection by antivirus software. Trojan.Packed.NsAnti detects a packer that is not known to be used for legitimate purposes.