Adware maker Zango has sued PC Tools, makers of the popular Spyware Doctor software, in a dispute over the way the antispyware program flags and removes Zango's technology.

Representatives from both Zango and PC Tools confirmed that Zango had filed suit against the antispyware vendor. However they declined to provide details on the lawsuit except to say that it involved a dispute over the way Spyware Doctor rated Zango's software.

"We believe the proceedings are an attempt by Zango to influence our reclassification process," PC Tools said in a statement e-mailed to IDG late Thursday. "Prior to the lawsuit we were well into an in-depth review and reclassification of the latest versions of Zango products," PC Tools said. "We advised Zango of this imminent re-rating and we believe they have chosen to lodge these proceedings as a way to gain media attention of the review."

The Spyware Doctor Starter Edition that ships with Google Pack assigns Zango an "elevated" threat-level rating.

According to a posting on a blog called Spamnotes.com, Zango is seeking at least $35 million in damages, alleging that Spyware Doctor removes Zango's software without warning users that it will be deleted. The lawsuit was filed Tuesday in King County Superior Court in Seattle, according to Spamnotes.com.

Formerly known as 180solutions, Zango is trying to clean up its tarnished reputation. In November it paid $3 million to settle U.S. Federal Trade Commission charges that its software was being installed deceptively on PCs.

PC users have complained that the software has been installed without warning, forcing them to endure unwanted pop-up ads. The company has also been accused of tracking user behavior and making its software too difficult to remove.

Zango now bills itself as an online media company whose products are critical to the Internet.

Critics are not so sure.

"Zango has exhibited numerous bad behaviors over the past few years," said long-time Zango critic Ben Edelman, an assistant professor at Harvard Business School. "I'd be interested to learn what specific descriptions Zango believes were false; in my view, most negative assessments of Zango have strong basis in fact."

After testing Spyware Doctor, Sunbelt Software Director of Malware Research Eric Howes said that Spyware Doctor clearly notified users before attempting to remove it. "It's similar to the way all antispyware and antimalware works," he said.