Dropbox Inc. has hit Synchronoss Technologies Inc. with a lawsuit claiming its rival in providing consumer cloud backup services infringes three Dropbox-held patents.

The patent infringement lawsuit was filed Wednesday by lawyers at Baker Botts in U.S. District Court for the Northern District of California, a venue where a separate patent suit filed by Synchronoss more than three years ago against Dropbox is currently proceeding.

Dropbox’s lawsuit claims all three patents are infringed by the Synchronoss Personal Cloud, a so-called “white-label data back-up and transfer solution,” which allows service providers such as Verizon to offer customers their own rebranded service.

The Dropbox patents claim to cover back-up and transfer of mobile data without the need for manual entry or plug-in to a “cradle” device, an interactive method for determining what items have been backed up and which still need to be uploaded, and a process for determining how much authentication and encryption a user needs for any given task on a specific network. Dropbox appears to have acquired two of the three patents it’s asserting from Intellectual Ventures since Synchronoss filed suit in March 2015.

A spokesman for Synchronoss said Thursday that the company doesn’t comment on “pending or ongoing litigation.”

Baker Botts and Dropbox declined to comment.

Dropbox’s offensive comes after Synchronoss’s three patents survived a motion to dismiss in 2016, which argued they covered patent-ineligible subject matter under the U.S. Supreme Court’s Alice decision.

U.S. District Judge Haywood Gilliam Jr. of the Northern District of California, who is overseeing that suit, found the claims of the Synchronoss patents “are directed to improving the manner in which computers synchronize data between devices connected to a network, by making that process faster, reducing the amount of bandwidth and storage space used, enabling synchronization across different data formats, and enabling synchronization without requiring devices to be physically connected.”

The U.S. Patent and Trademark Office’s Patent Trial and Appeal Board turned back Dropbox’s inter partes review of the Synchronoss patents last year. This month, U.S. Magistrate Judge Kandis Westmore, who is overseeing discovery in Synchronoss’ lawsuit, granted the company’s request to amend its infringement contentions following its inspection of Dropbox’s source code. A team from Dentons represents Synchronoss in that suit. Dropbox is being defended by counsel from Taylor & Patchen and Williams & Connolly.

Read the Dropbox complaint below: