Are you a human or a computer?

Over the Internet, it's getting harder and harder to tell.

Some of the common tests used by Web sites to distinguish between legitimate flesh-and-blood visitors and malicious human-mimicking computers recently appear to have been outwitted.

Last month, the human-verification tests, which typically require users to identify deformed letters set against a cluttered backdrop, were broken by a computer. The computer then repeatedly created free Hotmail e-mail accounts and sent spam from them, according to Websense, the security firm that detected the hacking.

The attack followed similar ones this year against Microsoft's Live Mail accounts and Google's Gmail service. A little over a week ago, the security firm reported a similar attack on Google's Blogger, a blog-publishing system.