I just got hit with the Conduit virus.
(and I never get them.. So crap)
It seems to replace (at least) 404 errors with a conduit search box which looks harmless. BUT DO NOT USE IT.. get rid of it right away
From botcrawl.com (which seems to be a pretty comprehensive site for fixing these kinds of problems):
Conduit is essentially documented as a browser hijacker, that installs onto a computer system and attaches to an internet browser, in order to change internet browser settings such as the home page and default search engine. This causes infected internet browsers to start up on search.conduit.com and redirect to search.conduit.com.