Well, this is certainly new.
Hackers in GTA Online have been able to cause all kinds of mayhem with various paid mod menus. We say "hackers" simply because it is shorter than saying "immature children buying mod menus with their parents' credit card" each time we refer to them, but you can be certain that 99.9% of the people you see hacking in Online didn't actually code the hack themselves (not that doing so would make it okay...).
Ranging from the regular stuff like spawning cash, instantly killing everyone in the lobby, spawning limitless props to crash the session all the way to stealing player's cash through insurance fraud (which thankfully has been fixed), hackers have been reported doing pretty much everything in the game that legit players are prevented from for the sake of balance.
However, hackers unlocking DLC before the official release date is something never before seen. A player has reported on a GTA Online related Subreddit that they have encountered a Prototipo, one of the recently leaked but not yet released DLC cars, in a race.
Other players have responded to the thread explaining how this would work in theory and another player also posted screenshots of encountering such a vehicle in game. This seemingly proves that this isn't a case of someone using a car skin mod Online and quickly documenting it before being detected.
The player driving the Prototipo claimed that he is a "Rockstar Beta Tester" putting the car through its paces before launch. However, seeing as that isn't actually a thing (definitely not in public lobbies, at least), it was probably someone with more than a little tech know-how unlocking the car in advance.
Seeing as the Prototipo driver was killed several times and didn't use any hack other than the car itself, it is safe to assume that we're not dealing with a malevolent scripter running a paid mod menu, rather someone who actually knows their way around game files and tunables finding a "backdoor" to walled off content.
As innocent as this action was, it is still technically "illegal" by Rockstar's terms. Some of the commenters in the thread also claim to have tried the car out. While you should probably take everything in the thread (and this whole story, really) with a few metric tonnes of salt, players are claiming that while the car is incredibly fast, it has some handling issues and poor traction.
