A WebmasterWorld thread has several webmasters complaining about how Yahoo Search handles 404s.

There is a really good analysis by Frank Rizzo, a senior member from 2002 at WebmasterWorld, who shows how Yahoo is doing three weird things on his site, in regards to 404s. He said Yahoo is showing:

Genuine 404s from pages which were deleted a while ago.404s from what seems to be badly configured software404s from what seems to be attempts at exploits.

Others are reporting similar issues as of this month and some are even thinking about blocking Yahoo’s spiders over the issue.

Forum discussion at WebmasterWorld.