A Webmaster posted a thread at Google Webmaster Help groups asking why his description for his site shows porn related terms in the snippet. The clear answer was that his site was hacked.
The question was posed by a concern webmaster:
The description showing on google for etceteraonline.eu is for a porn site, the link works fine but the description is wrong and not contained on my site please help.
Several top contributors replied, showing that the site was hacked and had tons of porn content on it. Here is the first response by Aaron:
you had most likely been hacked.
i see the indexed content as well:
Google has pulled the site a few hours ago, but you can see the concern this webmaster had that his site was showing up as a porn site in Google. Not only is it upsetting to the webmaster, it would also be very upsetting to the unsuspecting searcher. Plus, who knows if this site had malware that can infect one's computer.
These are one of the many reasons why Google acts so fast to remove hacked sites from the index. And we all know Google reincludes hacked sites after they are patched, fairly quickly.
Forum discussion at Google Webmaster Help.