The FBI is investigating a series of electronic sabotage attacks which have disrupted some of the world's most popular websites.

Online auction house eBay.com, Amazon.com and CNN.com became the latest victims on Tuesday afternoon following attacks on Yahoo and buy.com.

As in the previous cases, outsiders bombarded the sites with a huge number of nuisance messages making it difficult or impossible for legitimate customers to get through.

The electronic onslaught is termed a "denial of service" attack.

Embarrassing timing

However, it has not been confirmed whether the incidents are all the work of the same group of saboteurs.

The attack on buy.com appears to have been timed to coincide with the company's initial public offering on the stock market.

The blitzing of eBay may have been planned to embarrass the firm as it unveiled a venture with the Walt Disney Company's go.com to develop sites to sell movie props and other memorabilia.

All the companies said the saboteurs did not gain access inside their computers or retrieve information about their customers.

'Seriously affected'

However, the chaos highlights the vulnerability of even the best-protected websites and could shake public confidence in the booming global e-commerce economy.

Buy.com chief executive Greg Hawkins described the sabotage of his company's site as "an outside co-ordinated attack to our network that prevented access to our system".

CNN said its site had been "seriously affected".

It fell under attack for nearly two hours before technicians were able to shield its computers from the saboteurs late on Tuesday night.