Google's massive profits are largely generated from search advertising, where the adverts that appear beside the 'natural' results are related to the query typed into the search engine.
Advertisers pay a premium for that advertising because it can be so easily targeted to potential customers. They bid on keywords and the highest bidders' ads appear beside search listings.
A growing number of companies have filed suits against Google claiming that their brands are being hijacked by rivals. They argue that rivals' sponsorship of their brands is trade mark infringement.
Rosetta Stone has now filed such a suit, claiming that Google profits by diverting people who seek Rosetta Stone products and services away from them and towards rival services. Internet law expert and US academic Eric Goldman is tracking the suits and claims that Rosetta Stone's is at least the ninth such suit to be filed in the US.
"Google has in fact sold to third-party advertisers the 'right' to use the Rosetta Sone Marks or terms confusingly similar thereto as part of Google's search engine-based advertising program," said the suit. "As a result, Google's programming utilizes the expressed interest of web users in the Rosetta Stone Marks to trigger advertisements to websites that are not Rosetta Stone websites, some of which even compete with Rosetta Stone."
"In face, many of Google's 'sponsored links' are expressly designed to draw consumers away from Rosetta Stone websites," it said.
The suit claims that Google's practice forces Rosetta Stone into paying it to keep consumers from being confused.
"These unauthorized 'sponsored links' appear in close and confusing proximity to both the listings generated by Google's purportedly 'organic search results' system and the 'sponsored links' that Google forces Rosetta Stone itself to purchase to reduce the likelihood that web users will be diverted to other websites," said the suit.
Google's policy in the US has long been that companies can pay to have other companies' trade marks as 'triggers' for their ads, but that the trade marked terms must not appear in the ads themselves.
It extended that policy to the UK and Ireland last year, and to another 190 countries earlier this year.
This year it said that US firms could include others' trade marks in the body of ads as long as the company sold the goods in question.
In 2006 A New York court threw out a case arguing that the use of a trade mark as a trigger was trade mark infringement. A previous case had been settled out of court.