websense.com/securitylabs/blog ...

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Websense Security Labs has discovered that Google’s popular web mail service Gmail is being targeted in recent spammer tactics. Spammers in these attacks managed to created bots that are capable of signing up and creating random Gmail accounts for spamming purposes.

Websense believes that from the spammers’ perspective, there are four main advantages to this approach. First, signing up for an account with Google allows access to its wide portfolio of services. Second, Google’s domains are unlikely to be blacklisted. Third, they are free to sign up. And fourth, it may be hard to keep track of them as millions of users worldwide are using various Google services on a regular basis.

Don't you think that they'll update their Captcha services?