The modders behind the FiveM mod—which provides an alternative online playspace for the PC version of Grand Theft Auto V—claim that publisher Take-Two sent private investigators to their home in order to forcibly shut down the project.

The FiveM mod drew the ire of GTA V developer Rockstar Games earlier this year. The publisher blocked the modders' Rockstar Social Club accounts, barring them from playing the game or any other Rockstar titles associated with the account.

"The FiveM project is an unauthorized alternate multiplayer service that contains code designed to facilitate piracy," Rockstar said in a statement at the time. "Our policy on such violations of our terms of service are clear, and the individuals involved in its creation have had their Social Club accounts suspended."

However, the modders continued to work on FiveM despite Rockstar's ban. Allegedly, this has led to Rockstar sending two PIs the modder's home, demanding that development on FiveM should stop.

"I just got a pair of PIs at my door claiming to be sent by Take Two, handing me a phone with a person somewhere in the UK, or US, or whatever to 'discuss how to cease my activities with regard to Grand Theft Auto' and that 'they know what happened before with Activision and want to not get the lawyers involved at this time,'" reads the modder's post over on Reddit.

"However, they 'have tested their legal standing already and are quite certain of their point' and 'aren't willing to accept any solution other than ceasing my activities'. Oh, they also 'couldn't disclose any conversations they're having with other modification developers', didn't want to talk about general modification policy as 'it was just about my case,' and admitted they 'looked through my source code.'

The FiveM project has proven popular with a small subset of GTA V players, who value the access to dedicated servers that are separate from the centralised, semi-persistent competitive/co-operative space of Grand Theft Auto Online. A similar mod, "GTA:Multiplayer," received its own separate cease-and-desist from Take-Two and has since shut down.

"Take2 Interactive Inc. have contacted us and they asked us to stop GTA:Multiplayer, because from Take2’s point of view GTA:MP is a rival of their business," reads a statement on the GTA:Multiplayer website. "Grand Theft Auto and all its content is produced by Rockstar Games Inc. and published and owned by Take2 Interactive Inc. We, as developers, respect other developer’s intellectual property and their legitimate interests."

At the time, it was believed that GTA:Multiplayer might skirt around Rockstar's modding policy—which only allows for single-player mods—by being developed from the ground up, layering new multiplayer netcode on top of the single-player portion of GTA V. FiveM instead reverse engineered the game's own native network code on the client side and redirected it to dedicated servers.

The modders behind GTA:Multiplayer claim that they were in contact with Rockstar Games during the making of the mod and "got feedback from them." They instead hint the takedown came from publisher Take-Two directly. "We have never endorsed piracy, in fact we encouraged the buying of the game and never touched Rockstar Social Club as other modifications did or still do," reads their statement. "We were close to a release, but unfortunately we were not able to make it."

After Rockstar originally banned the FiveM modders' Rockstar Social Club accounts, Law of the Game blogger and attorney Mark Methenitis told Ars that Rockstar likely has some valid legal claims against the mod makers for "facilitating piracy." Aside from violating the Rockstar licence agreement, the modders could also face legal challenges under the DMCA's anti-circumvention language. This prohibits workarounds for "a technological measure that effectively controls access to a work."

"There's a pretty clear argument to be made that this is circumventing the measure to control access to GTA Online," Methenitis said. "Though a trial might get into some pretty nitty gritty technical details to determine what 'access' means in this context. It's also hard to say how the reverse engineering exemption might play in here. Considering the main [license-based] infringement claim is a slam dunk for violating the license, the DMCA claim may not be worth the time."