In his study, Edelman compared TRUSTe certified websites with a list of known malware sites from McAfee's SiteAdvisor service that blacklists websites containing spyware, spam, viruses and online scams. 

Using a base sample of 500,000 websites, Edelman determined the number of sites that have TRUSTe certification and cross-checked those against the McAfee list.

He found that 5.4 per cent of the TRUSTe sites were considered untrustworthy. Only 2.5 per cent of the sites from the base sample were blacklisted in SiteAdvisor.

Edelman alleges that TRUSTe has no incentive properly to verify compliance with privacy standards.

"Writing tough rules isn't easy, and enforcing them is even harder," Edelman wrote in a blog posting.

"Hard-hitting rules are particularly unlikely when certification authorities get paid for each certification they issue, but get nothing for rejecting an applicant."

TRUSTe responded that the organisation disagrees with Edelman's findings, stressing that the certification process is thorough and specific.

"Saying that our sites are more untrustworthy is a stretch," Carolyn Hodge, marketing director at TRUSTe, told vnunet.com. 

The organisation challenged the notion that Siteadvisor's blacklist provides an accurate overview of websites that should be considered untrustworthy.

The group also pointed out that Direct-revenue is no longer certified and that Webhancer will be required to submit its software for certification to a forthcoming Trusted Download programme.