Matt Cutts explains in his long post how Google tried to alert him and even indicated the problems detected by GoogleBot.
Ultimately, each site owner is responsible for making sure that their site isn't spammy. If you pick a bad search engine optimizer (SEO) and they make a ton of spammy doorway pages on your domain, Google still needs to take action. Hacked sites are no different: lots of spammy/hacked sites will try to install malware on users’ computers. If your site is hacked and turns spammy, Google may need to remove your site, but we will also try to alert you via our webmaster console and even by emailing you to let you know what happened. To the best of my knowledge, no other search engine confirms any penalties to sites, nor do they email site owners.
The discussion is interesting and can teach you a thing or two about Google's guidelines and what happens when something goes wrong, even if it wasn't your fault. I think this is an excellent exercise of communication from a company that has been accused of having too many secrets.
