Earlier this month, Grand Theft Auto V's main modding tool, Open IV, was shut down following a Cease and Desist order from Take-Two, Rockstar Games' parent company. Take-Two and Rockstar claimed that the tool was being used to negatively impact Grand Theft Auto V's online mode and was, therefore, ruining the experience of other players. There's been a lot of back and forth on whether this is true due to the fact that OpenIV is intended to be used only as a single player modding tool and not online.
Due to a bunch of little things in the game's files and other various things, it was deemed that Rockstar's anti-cheat system could flag people who had used OpenIV even if they were only using it for single player. After an overwhelming amount of backlash which consisted of online petitions and negative user reviews on Steam, Rockstar loosened up on their perspective stating that they were in contact with OpenIV and Take-Two to make things right and it appears they have done just that.
Today, PC players can go install OpenIV once again with not trouble at all. It was rendered useless after the Cease and Desist order and no one could access it but now it has returned in its full glory. It's currently unclear how this will affect mods and OpenIV going forward. We don't know if Rockstar has implemented new systems to make it more easy to detect who is genuinely hacking/modding the online portion versus those just modding the single player which Rockstar has actively promoted in the past.