Apple Inc in a latest development appealed a copyright case it lost against security startup Corellium, which helps researchers examine programs like Apple’s planned new method for detecting child sex abuse images.

A federal judge last year rejected Apple’s copyright claims against Corellium, which makes a simulated iPhone that researchers use to examine how the tightly restricted devices function.

The news comes from Reuters, which claims that the notice of appeal was filed today with the U.S. District Court for the Southern District of Florida. This follows an initial settlement between Apple and Corellium that happened earlier this month, so it’s unclear why Apple is now sending a notice of appeal in court regarding the same case.

Corellium sells tools to allow security researchers access to a “virtual” software-based version of the iPhone. In its suit, Apple alleged Corellium violated copyrights to its iOS operating system.

The appeal came as a surprise because Apple had just settled other claims with Corellium relating to the Digitial Milennium Copyright Act, avoiding a trial.

Apple has been fighting Corellium since 2019 after the company released a tool that is capable of virtualizing iOS software. While Corellium says the platform is focused on security researchers, Apple argues that the company is infringing copyright on its software.

In December 2020, Apple faced a major defeat when a federal judge ruled that Corellium made “fair use” of the iOS code, but the Cupertino-based company continued to seek an injunction against Corellium’s platform. Terms of last week’s settlement were unknown, but Corellium sent an email to its sales team saying its platform would remain available for sale.

Security experts are among Corellium’s core customers, and the flaws they uncovered have been reported to Apple for cash bounties and used elsewhere, including by the FBI in cracking the phone of a mass shooter who killed several people in San Bernardino, California.

Apple makes its software hard to examine, and the specialized research phones it offers to pre-selected experts come with a host of restrictions.