Avira, which re-affirmed its right to classify Freemium.com as a nuisance back in June, has launched a legal offensive against the controversial app.

The security software firm's filing concerns Freemium.com's alleged practice of “confusing users into installing unwanted programs that can compromise users’ privacy or weaken their computers’ security.”

The German lawsuit represents a rare, if not unprecedented, case of a security vendor taking a software publisher to court over this business practice.

Developers of software classified as unwanted or deceptive periodically take security software vendors to court, with one of the most high profile cases involving a series of unsuccessful lawsuits by Zango against Kaspersky Lab and others over adware classification between 2007 and 2009.

German law is pretty tough on protecting consumer rights and privacy, hence Avira's decision to go after Freemium.com in its native country. Avira further argues that Freemium.com infringes German privacy laws because of the way its technology sucks up all sorts of data, something the complainant argues constitutes an unfair business practice.

“It is time to take the fight against this next-generation adware directly to the source,” said Travis Witteveen, chief exec of Avira GmbH, in a statement. “Freemium.com is engaged in unfair competition that violates consumers’ legal right to privacy and uses invalid contracts.”

Freemium.com has yet to respond to our request to comment on Avira’s lawsuit. We’ll update this story as and when we hear more.

According to Avira, Freemium.com uses a software installation tool or “wrapper”, which itself is a PUA ("Potentially Unwanted Application”). The app uses social engineering tricks to make the user install other potentially unwanted applications in addition to the initial desired software - and the user is not even aware of this. “It’s like putting ten layers of wrapping paper on a single present– there’s room for a lot of unpleasant crapware to be hidden,” Witteveen explained. “We’ve documented where a user wanting to download a single app could end up with four additional programs, two browser extensions, and a desktop link to a gaming site.”

The end-user licence agreements (EULAs) governing customers’ relationship with these apps range from invalid to nonsensical, Avira contends. “One extreme example was a German corporation using English language contracts filed under Egyptian laws for German consumers,” noted Claus Kaufmann, general counsel at Avira. “The data use policies give apps virtually unlimited rights to sell and share information about consumers, record data use, and track locations.”

Freemium.com previously took Avira to court – and lost – over Avira warning users that many of the site’s apps were “potentially unwanted apps”.

Avira has sent our customers more than 225 million PUA warnings over the last seven months alone.via technology such as PUA Shield, which comes fitted to the Avira Browser Safety plugin. ®