Well I’ve long suspected it and now Matt Cutts has confirmed it: sites that get hacked are removed from Google’s index.
Turns out the removal occurred for security reasons shortly after Ryan’s site was hacked. Here’s an extract from Matt’s comment on Ryan’s blog about the situation:
“Sorry to hear that your blog got hacked. I know that it’s disappointing if you don’t show up in Google, but there’s another way to look at it. It looks like your blog was hacked to show “buy pharmacy”-type links, but what if the hackers had hosted malware on your site? Then every user to your site might have gotten infected just by visiting your site. That danger to Google users is one of the reasons that we temporarily remove hacked sites from Google.”
So be warned, if your site is hacked, you might want to keep an eye on your Google Webmaster Tools account and submit a re-inclusion request as soon as things are back to normal.