Update 3: Lead developer of OpenIV shared a few more details about the timeline of events. From his updated post:

"To make it all clear, here is what happened:

1 - At May 19th, 2017, I received an email from the legal counsel for Take Two Interactive in the USA. In this email they has requested to stop immediately any further work and/or distribution of OpenIV and "Liberty City in GTAV" projects.

2 – In belief, that we did not violate any laws, I asked them to provide more detailed information about their request. They agreed to provide details by email.

3 – On June 5th, 2017, after two weeks of silence, I got C&D letter from lawyers company (legal representative of Take Two in Russia), both in electronic and paper form, to my employer address. This C&D accuses me in Russian laws violations.

4 – After many heavy thoughts, we had decided to agree with their claims. We did not make it easily; it is very hard decision for us."

Update 2: Rockstar has sent PC Gamer a brief official statement on the matter:

"Take-Two's actions were not specifically targeting single player mods. Unfortunately OpenIV enables recent malicious mods that allow harassment of players and interfere with the GTA Online experience for everybody. We are working to figure out how we can continue to support the creative community without negatively impacting our players."

Update: I've communicated with GooD-NTS via email and I believe this to be a legitimate legal notice sent on behalf of Take-Two. I've also received word from Rockstar that a statement will be issued "shortly" but I have not received it yet. I will update this story again if and when I receive the statement.

Original story: The developers of OpenIV, a popular modding tool for the Grand Theft Auto series for nearly a decade, posted today on the site gtaforums.com, claiming they received a cease and desist letter from Take-Two Interactive. According to the post written by OpenIV lead developer 'GooD-NTS', the C&D arrived on June 5 and claims that OpenIV allows "third parties to defeat security features of its software and modify that software in violation Take-Two's rights."

OpenIV is an editor and archive manager for GTA 4 and 5, and Episodes from Liberty City, as well as Max Payne 3. It was first released in 2008, and has been an essential tool for both the creation of GTA mods and for installing and playing them. However, the developers of OpenIV say they've decided to halt distribution of their modding tool due to the C&D.

"Going to court will take at least few months of our time and huge amount of efforts, and, at best, we'll get absolutely nothing," the post says. "Spending time just to restore status quo is really unproductive, and all the money in the world can't compensate the loss of time."

OpenIV was discontinued due to Take Two Interactive request.https://t.co/GZZk4G9WFf#OpenIV #GTAV #GTAIV #RDR #MaxPayne3 #modding #RIPJune 14, 2017

The post continues: "It was a hard decision, but when any modding activity has been declared illegal, we can't see any possibilities to continue this process, unless top management of Take-Two company makes an official statement about modding, which can be used in court."

I've attempted to contact Take-Two via email and phone to both confirm it sent a C&D and to provide me with a comment, though I have not yet received a response.