Malware -- surreptitious software capable of stealing sensitive information from your computer -- is increasingly spreading over the web. Visiting a compromised web server with a vulnerable browser or plugins can result in your system being infected with a whole variety of malware without any interaction on your part. Software installations that leverage exploits are termed "drive-by downloads". To protect Google's users from this threat, we started an anti-malware effort about a year ago. As a result, we can warn you in our search results if we know of a site to be harmful and even prevent exploits from loading with google desktop Search.
(Google Online Security Blog)

I think it is both good and necessary that a big and influencial company like google is thinking seriously about implementing security measures. There are, of course, a couple of things you clearly should not do on the net, but I meet more and more people that have absolutely no clue about the internet : They don't know what it actually is and they will typically trust anyone on it because they are there, rite ? As if some governmental agency checks and approves everyone who wants to go online....And even then, who trusts the government after having seen enemy of the state ??