The European Commission is investigating Google to see if it has broken competition and anti-trust laws.
A UK price comparison site called Foundem, a French legal search engine ejustice.fr and Microsoft have all complained that Google tweaked search results unfairly to push them further down the rankings than they should be.
Google said it would cooperate with the probe and hand over information to the Commission. The company said: "we are confident that our business operates in the interests of users and partners, as well as in line with European competition law."
The search giant used a blog post to dismiss the complaints as an inevitable result of its success.
It said some vertical search engines like Opodo, Expedia and Moneysupermarket.com tend to rank highly in its rankings.
Google said it had a good relationship, and AdSense deal, with price comparison site Ciao! until it was bought by Microsoft for $500m in 2008. After that Google began getting complaints that the site was breaking its Ts&Cs.
The search and advertising giant obviously hopes to generate some sympathy by going public with the complaint in this way. But the tone of the post may not win over every doubter: "our search is not perfect, but it's a very hard computer science problem to crack. Imagine having to rank the 272 million possible results for a popular query like the iPod on a 14 by 12 screen computer screen in just a few milliseconds. It's a challenge we face millions of times each day."
Google's full blog post is here.
We'll have more on this story later today, there's more on Foundem's problems here. ®