Judge Leonie Brinkema dismissed a motion filed by Google and Overture to dismiss the case, which charges that Google and Overture violated Geico's trademark by selling advertising, or "sponsored links" to Geico's name. If successful, the lawsuit by Geico could hobble the engine that has fuelled Google's growth: search advertising.

Sponsored links are key for both Google and Overture, which is owned by Yahoo. The companies sell advertisers the right to have links to their web pages appear, under a separate heading, when certain keywords appear in a search. In a public filing on 29 April, linked to the company's plans to sell stock in an initial public offering, Google disclosed net income of $105.6m (£59m) and revenue of $961.9m in 2003.

Geico sued both companies for selling rights to its trademarked name to advertisers, alleging trademark infringement, false representation and trademark dilution under a federal trademark statute known as the Lanham Act.

Google and Overture claimed that they could not be sued for trademark infringement because they used Geico's name only in internal computer algorithms that determined the sponsored links to display, and did not identify the search engines as the source of the Geico product or imply an endorsement by Geico.

In the ruling, which was filed on 25 August but not publicised by the companies, Judge Brinkema rejected those arguments, saying that Google and Overture's sale of adwords for sponsored links may make the companies liable for unlawful use of Geico's trademark, according to a copy of the decision.

The judge refrained from ruling on whether the sale of adwords actually violated the Lanham Act or Virginia law, saying "that decision cannot be reached until discovery has been completed".

In the same decision, the judge threw out two other Geico charges.

A claim by Geico of "tortious interference" with Geico's business was found to be too broad. Another claim of "statutory business conspiracy" between the search engines and their customers were not well supported enough to prove that the companies conspired to injure Geico.

"The fact is" says Quantos's Colin Hiom "that companies throughout the internet may well be infringing on others trademark material".

"If in doubt, leave it out - is the advise we give our clients.

However, if the boot is on the other foot and you need to review trademark and copyright material belonging to your company in this context please call either Colin Hiom or Quantos legal associate Tony Morris, LLB, direct on 0207 209 2093.