There was a marked decrease in global website defacements in the period after 11 September, according to security watcher mi2g Intelligence Unit.

But hacking has now begun to rise again, with 79 overt attacks reported in the first 24 hours of 2002.

DK Matai, chairman and chief executive at mi2g, put the sudden drop in September down to the US Department of Justice linking hacking to terrorism through the Surveillance and Anti-terrorism Bill submitted to Congress on 19 September.

He said that the number of sites defaced globally had risen fourfold from 7,629 in 2000 to 30,388 in 2001. May alone had produced a staggering 3,853. In September the figure plummeted to just 811.

The majority of defacements (63 per cent) occurred on servers running the Microsoft Windows and Microsoft IIS/PWS combination, and 18 per cent were attacks on the Linux with Apache combination.

"Website defacements cannot be dismissed as electronic graffiti," explained Matai. "Most hacking takes place because of incomplete security policy and implementation.

"The best way to ward off the threat from hackers is to keep the personnel policy and systems security architecture continuously up to date."