The number of high-profile distributed denial of service (DDoS) attacks reported in the first seven months of 2002 has reached more than double the total number publicised through the whole of last year.

This year's victims include the websites of the Dutch royal family, internet network company Tiscali and the Pakistan Government.

DDoS attacks flood web servers by repeatedly sending bogus traffic packets, causing websites to become inaccessible.

Virus-spreading email worms are also blamed for installing attack software on attacked PCs, which can then be activated by DDoS attackers.

Neil Barrett, technical director at information security consultancy Information Risk Management, said the large increase was due to more high-profile companies reporting incidents.

"It is becoming more and more acceptable to report [attacks] to the press and police because it is no longer seen as a failure," said Barrett.

He added that there was a trend towards using DDoS attacks, and the threat of further attacks, for extortion campaigns on ecommerce websites.

The ease of carrying out attacks had also increased. "The tools to carry out DDoS attacks are widespread and the chances of being caught are very low," Barrett said.