Websites offering fake antivirus software are prominent in a new '100 Dirtiest Websites of 2009' list compiled by Symantec.

The security firm used its website safety rating service, Norton Safe Web, to compile a list of sites available on the web today that contain the most threats.

The average number of threats per malicious site is 23, but those that made the list have a staggering average of 18,000 threats per site.

In fact, 40 of the 100 dirtiest websites have more than 20,000 threats per site and 75 percent have distributed malware for more than six months.

Symantec's Dirtiest Sites 2009

Symantec says that visiting one of these sites, without downloading or clicking on anything in particular, could put you at risk of exposing your computer to infection, and worse, put your identity, personal and financial information into the hands of cybercriminals.

Multimedia sites and adult sites also feature heavily in the list. However, the remainder of the dirtiest sites cover subjects ranging from laser engraving and gaming cheats, news sites and glove retailers.

The US hosts the majority of these 'dirty sites' but was closely followed by China, Germany, Canada and the UK.

"As the results suggest, online threats are constantly evolving as cybercriminals continue to look for sneaky and more complex ways to trick people into giving out personal details, targeting their money, identity and assets," explains Con Mallon, EMEA consumer product marketing director.

Symantec said it has chosen not to publish the list due to the explicit nature of the URLs.

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See also: Symantec reveals the web's 100 dirtiest sites