Am not sure.  But an ASCII printable string certainly should not be used to judge whether a virus is one or not.  At the very least, it should base judgements on binary strings.  I would say that hashing is perhaps more reliable.
Though I've never trusted AV anyway, since it's extremely easy to bypass.  With the above example, if that string really is what it looks for, simply changing it gets this "virus" past your AV.