The US Federal Bureau of Investigation (FBI) is focusing on California and Oregon as potential locations for hackers that attacked a raft of Internet sites this week, including Yahoo and eBay.

The FBI has already seized a computer at the University of California in Santa Barbara after determining that it may have been used to send out socalled daemons to bombard websites with fraudulent queries, so bringing them to a standstill. This type of attack is dubbed "distributed denial-of-service".

But an FBI official emphasised that the current focus of the investigation on the two western states does not mean that other locations have been ruled out as origins for the attacks.

The action came as US President, Bill Clinton, invited top executives from about 20 companies, including Cisco and Yahoo, to a White House meeting on Tuesday. The aim is to discuss long term plans about how to prevent further attacks and to examine whether existing cash being put into computer security is being channelled in the right way.

Attorney General Janet Reno, National Security Advisor Sandy Berger and Commerce Secretary William Daley will also be among those attending.