A free security tool has been downloaded more than 38 million times since it was launched 12 months ago. McAfee SiteAdvisor is an internet scorecard application which rates potential risks on websites.

SiteAdvisor integrates with Firefox and Internet Explorer. It applies 320 million daily potential risk ratings to websites for search results, browsing and e-transactions, and is based on scanning results for spyware, adware, exploits, excessive pop-ups and spam.

SiteAdvisor staff analyse and collate data retrieved from website scans and from user volunteered feedback to produce a scorecard indicative of the potential dangers of a given site.

McAfee's Monica Kelly said the high adoption rate reflects the increasing need for online security.

"SiteAdvisor has enjoyed very strong adoption since its launch last year and has demonstrated the urgent market need for this technology," Kelly said.

SiteAdvisor is available to users free of charge here.