The internet search giant Google is facing a bitter lawsuit against its rival search engine, Overture Services.

California-based Overture has filed for unspecified damages, after accusing Google of illegally using the technology it created to sell online advertising.

Overture pioneered the "paid listings" advertising model where companies buy certain search terms in order to ensure their name appears prominently when certain words are entered in the search engine.

While other forms of Internet advertising have floundered, the paid listings model has flourished.

Overture's search results, are featured on several high-profile sites such as Yahoo and AltaVista.

Overture - which was formerly known as goto.com - filed a lawsuit over the same issues against a smaller search engine, FindWhat.com, last year.

Profitable

Google spokeswoman Cindy McCaffrey has denied allegations of patent infringement.

The privately-owned dot.com is expected to achieve sales of about $50m this year.

The group claimed that it had become profitable last summer, but it is not obliged to reveal financial data to the stock markets since it is not a listed firm.

Plans for a future flotation have been raised, but no timeframe has been set.