Microsoft has filed what are believed to be the first lawsuits designed to stop the growing practice of malvertising

The company has filed five suits against unnamed individuals who it has accused of posting malicious and deceptive code through ads on its MSN advertising network.

The suits allege that individuals using the business names Soft Solutions, Direct Ad, qiweroqw.com, ITmeter INC, and ote2008.info used malvertisements to distribute the malicious software or present deceptive websites that peddled scareware to unsuspecting online users.

Associate general counsel Tim Cranton said that although Microsoft doesn't know the names of the specific individuals involved, by filing the civil suits in a US court it hoped to uncover the individuals responsible and prevent them from continuing to deploy malvertising.

"We hope that today's filings will help deter malvertising in the future," Cranton said in a blog post. The documents were filed in King County Superior Court in Seattle, Washington.

Malvertising is a technique where code is placed in an online ad to either mislead the user or infect their computer. Code might re-direct the user to a site that advertises rogue security software, or scareware, or it might install malicious code such as a Trojan on the user's PC, either infecting it with a virus or leaving it open to remote control by a hacker.

Malvertising is a growing phenomenon. An ad appeared on the New York Times web site last weekend that claimed to offer a virus scan and then prompted the user to buy scareware to fix the problem.

Among the allegations in its various filings, Microsoft has claimed breach of contract in placement of ads on the MSN network, fraud, and trademark infringement.

You can read more about the case and download Microsoft's filings here.