Packed.Generic.257 is a heuristic detection for a packer used by the following threat families:
A packer is a tool that compresses, encrypts or obfuscates executable files. Malware authors often use packers to conceal threats from detection by antivirus software. Packed.Generic.257 detects a packer that is not known to be used for legitimate purposes.
Files that are detected as Packed.Generic.257 are considered malicious. We suggest that any files you believe are incorrectly detected as Packed.Generic.257 be submitted to Symantec Security Response. For instructions on how to do this using Scan and Deliver, read Submit Virus Samples
Symantec Security Response encourages all users and administrators to adhere to the following basic security "best practices":