1. A system for executing computer virus definitions containing general purpose programming language extensions, comprising: a computer virus data file storing one or more virus definition records, each virus definition record comprising: an identifier uniquely identifying a computer virus; a virus detection section comprising object code providing operations to detect the identified computer virus within a computer system; and an extension sentence comprising object code providing reusable operations implemented in a general purpose computing language; and an anti-virus engine interpreting, for each virus definition record, at least one of the object code of the virus detection section and the extension sentence.