We all know how, er, viral these things are. You could possibly have a very good spyware/virus system set up for when the sales drones are inside your office, but if they hook up to a client's (or prospective client's) network to trot out $COMPANY's dog-and-pony show, that could be all that's needed. Bring laptop back to the office, and things would then be noticed.
It ain't always about the porn.