Evil Smiley Unexpectedly Appears on Front Page

Someone visting my blog reported that the front (index) page was “all covered with evil smileys” when he visited early this morning. I didn’t see it, but access.log confirms that his browser requested icon_evil.gif. access.log also shows three other isolated requests for the same file from other clients.

I am certain there are no entries or comments on my blog with an evil smiley emoticon code (:evil:). Even if there were, it wouldn’t make sense for the front page to be “covered” with them.

The user has not been able to reproduce the phenomenon, but it has left me worried. Could this be a sign of a compromised system? Is there any rational explanation for what happened?