Lodsys, the company pursuing high-profile patent infringement cases against many in the tech industry, is finding itself on the receiving end of a pre-emptive lawsuit challenging its patents.

ESET, a San Diego-based antivirus software maker, filed a declaratory judgment lawsuit (see filing below) on Friday against Lodsys with the U.S. District Court for the Southern District of California. The lawsuit, first reported by Florian Mueller of the FOSS Patents blog, seeks a declaration that its products do not infringe on Lodsys' four patents and to invalidate those patents.

Lodsys claimed in letters to ESET that the upgrade feature in the company's NOD32 Antivirus 4 software violated four patents held by Lodsys and offered to license the patents to ESET, according to ESET's filing.

ESET took the legal action after receiving threatening messages from Lodsys asserting it was infringing on Lodsys' patents. "Defendant's message enclosing the claim chart stated that defendant's goal was 'resolving this issue with a minimum of expense and hassle for your clients,'" EST said in its filing.

Representatives for Lodsys did not immediately respond to a request for comment, and a note on its site states that it does not address media questions.

Lodsys is what's known as a nonpracticing entity, or NPE, which means a company that licenses patents but doesn't actually have any other business. The company first attracted widespread attention in May when it sent letters to Apple iOS and Android developers notifying them that their mobile applications were infringing on four patents.

The group sought a percentage of each application developer's revenue, even threatening to go back to collect income that had already been earned. Apple responded that its licensing agreement with Lodsys covers its developers, a claim that Lodsys has rejected.

Previous tech targets have also included Samsung, Hewlett-Packard, Brother, and Motorola. But Lodsys broadened its legal attack on Friday to include Sam's Club, Best Western, Black & Decker, the Container Store, the Teaching Company, Vitamin Shoppe, Vegas.com, Adidas, CVS, and Best Buy.

ESET isn't alone in its pre-emptive efforts. A Michigan-based company called ForeSee Results filed a declaratory judgment suit against Lodsys. ForeSee names Adidas and Best Buy as clients that have received Lodsys letters asserting that they use technology covered by the patents.

Update at 9 p.m.: The New York Times Company and market research firm OpinionLab have filed similar lawsuits today against Lodsys in the U.S. District Court for Illinois. The New York Times' complaint states that Lodsys has accused the newspaper's Web site of infringing on its patents. OpinionLab's filing also accuses Lodsys of unfair competition and tortious interference.

ESET Declaratory Judgment Complaint Against Lodsys