A UK-based website that names and shames websites run by cyber criminals has been struck by a denial-of-service (DoS) attack, according to Sophos.

The security software vendor said a botnet is bombarding the Bobbear website with traffic, making it impossible for legitimate visitors to reach the site.

Bobbear administrator Bob Harrison told Sophos that the botnet is "huge" with "over half a million recorded zombie hits from midnight to 8am today".

"It's appalling to see cybercriminals launch such a dirty attack on a voluntary organisation that is actually doing something positive to make the internet a safer place - it just goes to show how unscrupulous these crooks are. The only consolation that Bobbear can take from this situation is that they must be having an impact on the fraudsters if they are prepared to go to such lengths to put the site out of operation," said Graham Cluley, senior technology consultant at Sophos.

Sophos also said that in 2007 hackers started a hoax email campaign designed to tarnish Bobbear's reputation by asking for money to be donated to the website via fraudulent online payment service e-Gold.