Are Hotlinked Images Now a Liability?

ConcernedImage asks: "I work for a company that has a strong online community, with a full set of message boards that currently allow external image hotlinking. With the new WMF exploit out there, all it takes is one user to link to a bad image, and suddenly it's -our- web site inflicting the computers of others (at least, as far as our users are concerned). Is allowing hotlinked images a legal liability now? What steps are other online communities taking to protect themselves and their users against this?"