Bungie has shut down Destiny 2's Trials of Osiris, the game's competitive PvP mode, over the weekend, but not because of a game-breaking bug or balance issues. It's been shut down because of an exploit that allows cooperating players to farm free flawless cards - gained by getting seven wins without a single loss - through die-rolling, character swapping, and a secret code.
This news came to light when YouTuber Lunarated posted a video where he mentioned getting plenty of free wins from fireteams using the Hakke emblem. Similarly, Twitter user @TrialsReport noticed an unusually high number of players getting flawless cards despite only bagging 0-5 kills, and cited Lunarated as where the first information came from, so presumably, that video inspired them to look into it. A bit of digging later and Lunarated discovered that there's a huge community exploit where people use Hakke banners to signify that they're in on this exploit. Lunarated calls this exploit the "China Casino Flawless Method" due to it originating in the China/Hong Kong area before its increased visibility caused it to be taken up by other players.
First, a three-man team queue for Trials with burner characters, two of which have Hakke upgrade emblems and one without, who represents the "messenger." The user enters and leaves the queue until they find another team in on the fixing. From there, a representative from each team contacts each other on Steam and rolls a die. The winner rejoins the game and switches to their main team while the loser backs out. This gives the winning team a free win while the losing team gets a loss on their burner characters. Eventually, this allows for flawless completion, giving access to the Lighthouse and the mode's top rewards.
As a result of all this, Bungie announced in a tweet that Trials is disabled for the rest of the weekend. The tweet doesn't mention any reason for disabling Trials, simply referring to "an issue." However, players with access to the Lighthouse, whether they gained legitimately or through win-trading, can still access it. Bungie has yet to mention anything about the exploit or the fate of Trials, but a hotfix releasing tomorrow may provide more answers.
The exploit is reliant on a system that allows players who get disconnected to rejoin, potentially with different characters, within a limited amount of time. Disabling this feature is likely the easiest way to stop the exploit, but disabling it would also be tough for players with an unreliable Internet connection.