blames Google for rogue ads, a firm formerly used by Google to verify the legitimacy of pharmacy advertisers, has blamed the search engine for allowing through rogue vendors.

It linked that failure to a US investigation that Google said earlier this week could cost up to $500m to resolve.

A second firm that was later hired by Google for the same purpose as disputed its claims, instead pointing the finger at for lapses that allowed illegal pharmaceutical advertising to find its way into the search service.

The rival accounts emerged days after Google revealed that it had set aside the $500m to resolve an investigation by the Department of Justice into ads “by certain advertisers”. It has given no further details of the case. A person involved in the case later told the Financial Times that it involved its acceptance of advertising from companies selling unlicensed pharmaceuticals. said in a blog post that it had adequately identified online pharmacies that should be allowed to advertise on Google and was not responsible for the fact some illicit advertisers still appeared online.

“Rogue online pharmacies that never applied to our program found a way to advertise on Google”, wrote vice-president Gabriel Levitt. “We were never the gatekeepers for Google; that remained their job.” Mr Levitt did not immediately respond to requests for additional comment.

However, John Horton, head of a competitor named LegitScript, told the Financial Times that he had identified multiple advertisers on Google that bore certification from PharmacyChecker, and which he suspected “were selling drugs without prescriptions even for controlled substances.” PharmacyChecker could not be reached for comment and Google declined to coment.

In 2008, US pharmacy regulators wrote to Google urging it to drop the firm it used to screen out illicit pharmacies, but did not identify by name. The unnamed firm had let through several advertisers “that source their prescription drugs from various locations outside of the United States … which is contrary to US law,” according to the letter from the national Association of Boards of Pharmacy.

Google tightened its policy for accepting advertising from online pharmacies in February 2010. At the same time, it dropped PharmacyChecker, which it had used since 2006, and turned to LegitScript to screen advertisers.

One result of the tighter policy was that some legitimate pharmacies have now been blocked from the search service, according to PharmacyChecker.

LegitScript had posted studies of problems it claimed to have identified at Microsoft and Yahoo and was beginning work on a study about Google when that company changed its practices and hired the firm.

Google declined to comment on the rival claims.

Copyright The Financial Times Limited 2017. All rights reserved. You may share using our article tools. Please don't cut articles from and redistribute by email or post to the web.