I don't buy into the claim that Google was hacked (which would require breaking into Google's system and planting the links directly into the Google index).

Gamed? Yes. Hacked? No.

Why? Because it is trivially easy to present different content to web bots and web browsers, after which you just have to fine tune the innocuous version that the Google web bot sees until it gets ranked highly. Once the sites are ranked highly (so as not to tip your hand too early), then you redirect web browsers to the malware sites.

Reading the blog over at Google Watchdog, it's obvious from what is being described that some variation of this is what happened.

There was no hacking of Google involved.