Puzzles could block mass computer attacks

Thursday, 15 May 2003, 11:22 AM EST

Setting computers a puzzle could thwart a type of mass computer attack increasingly being used to target websites, say US computer researchers.

Distributed denial of service (DDoS) attacks involve bombarding a web server with a flood of faked requests. This can prevent legitimate requests reaching a site and may crash the site's server. The attack is co-ordinated from thousands of previously hacked computers making very hard to identify and block the source of an assault.

DDoS attacks have become a popular method of online protest. The Arabic news organisation Al Jazeera saw its web site brought down after it broadcast and posted online images of US prisoners of war during the conflict in Iraq.

But forcing computers to solve a puzzle in return for access to a web site could provide a solution, says XiaoFeng Wang at Carnegie Mellon University in the US. At the IEEE Symposium on Security and Privacy on Monday, Wang presented research showing that this technique can control the number of requests a machine is able to send to a site.

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New Zeus variant targets users of 150 banks

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