As Twitter has been getting more and more popular, it is increasingly targeted by worms, spam and account hijacking.

We've recommended Twitter to start filtering traffic to fight this. They can easily do it, as all the messages go through them.

Twitter hasn't announced this, but we just noticed that they have now started filtering Tweets that contain links to known malware sites.

This is what it looks like if you try to send a message with a bad URL:



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Updated to add: A source tells us it is confirmed that Twitter's URL filtering is using Google's API.

However, we ourselves cannot confirm this to be the case based on our internal tests…