* Looks like your signatures only lists about 100 viruses. Why not use
the signature database from OpenAntivirus like ClamAV does?

Because I use perl regular expressions in signatures to detect polymorphic
virus or suspicious virus, and for speed I need the file to detect the
position of signature.

* Where is the signatures file stored for File::Scan?

The signatures are stored internally in Scan.pm file, but you can add new 
signatures to signatures.txt file in files directory and rebuild the 
module.

