BleepingComputer.com: Exploit Code Hiding In Cache Servers

Malicious code is living on weeks after it has been removed from websites thanks to an unexpected culprit - cache servers....According to Finjan Software...caching technology used by search engines, ISPs and large companies has been discovered to harbour certain kinds of malicious code even after the website that hosted it has been taken down.

Such "infection-by-proxy" code can remain in caches for as long as two weeks, giving it a "life after death" at a time it would conventionally be assumed to have been neutralised...