New York Attorney General Eliot Spitzer has gone after a company alleged to be one of the largest spyware distributors in the world.

Spitzer has filed a lawsuit that will force spyware distributor Direct Revenue to stop installing its software on PCs without their owners' consent.

The suit also aims to prevent the firm sending ads to existing PCs running its software, as well as forcing it to open its accounts to investigation.

"Surreptitiously installed spyware and adware harm consumers and businesses, and my office will continue to prosecute these practices aggressively," said Spitzer.

The Attorney General's office spurred industry-wide attention to this problem last year with a lawsuit and settlement against adware distributor Intermix Media.

"These applications are deceptive and unfair to consumers, bad for businesses that rely on efficient networks to do their jobs, and bad for online retailers that need consumers to trust and enjoy their online experience," said Spitzer.

"We will continue to side with consumers in their fight for control of their desktops."

Direct Revenue is accused of installing spyware alongside 'free' applications that promise to optimise PC performance, such as VX2, Aurora and OfferOptimizer. The suit alleges that the company makes it hard to find and remove its code.

For example, former Direct Revenue chief executive Josh Abram (a defendant in the lawsuit) boasted in an April 2005 email to a distributor: "We have a very stealthy version of our adware product which we're happy to give you. Don't worry. If we do a deal - a build together - these will not be caught."

Similarly, the company's chief technology officer observed in 2005 that users "don't know how they got our software (this is both upgrade and recent install) " and that users "say that they are getting so many ads that it is annoying them ".

The legal action also alleges that the company takes part in "drive-by downloads" which take place without any notice at all to consumers.

The Attorney General's office documented 21 separate websites through which this practice, known as 'bundling', occurred.

"We applaud Attorney General Spitzer for attacking this problem at its source and for sending a message that years of illegal behaviour will not go unanswered," said Ari Schwartz, deputy director of the Center for Democracy and Technology.

"Aggressive law enforcement is an essential component in the ongoing fight to stem the tide of unwanted spyware."

The suit arises under New York's General Business Law, which prohibits false advertising and deceptive business practices; its Penal Law, which prohibits computer tampering; and its Common Law which prohibits trespass.