Whatever you do; do NOT enable IP accounting or IP CEF on any ethernet interface. The virus activity will fill your memory within minutes and crash your router.
Best way to save your router is with an access-list applied to the ethernet interfaces. Find out which virus you are fighting, how it's propagated, and build your list to filter that activity. The latest nasty virus spread using ICMP and we built a filter to block ICMP echo, applied it on ethernet interfaces at all 300+ locations, then went machine-by-machine to eradicate.
Good luck!
Haveagoodun!
Nettekkie1010