Update, 14:24 on October 25: Bungie has posted a notice indicating that the approximately 400 bans issued were all handed out after manual investigation and that "overlay or performance tools" were not the cause. The original story follows below.
Destiny 2 is surely one of the bigger PC game releases this year. This is Bungie's first PC game since the release of Halo 2 about 10 years ago, and the launch has been fairly trouble-free. The game runs well even on modest hardware, and crashes are apparently few and far between. The only major problem we're aware of is a pretty sharp spike to step on, though: players are apparently being banned from Destiny 2 for unclear reasons. The current suspicion among the community is that the banned players were using screen overlay applications.
If the reports are true, the list of applications prompting bans includes popular streaming apps Open Broadcaster Software (OBS) and XSplit, performance tuning kit like Fraps, MSI Afterburner, and EVGA Precision, and even chat overlays like those for Discord and Mumble. Players have also claimed that they were banned over tools like Corsair's Utility Engine, NZXT CAM, and Razer Synapse. Obviously, all of these tools are harmless, but some of them rely on a technique called "code injection" that could make them difficult to differentiate from malicious modifications.
For its part, Bungie had a FAQ page posted way back on September 11 that warned users off the offending apps while playing Destiny 2. The FAQ does not explicitly state that users would be banned, but instead refers to these applications as "incompatible." Whether the applications and the issued game bans are related is still up in the air, but a separate article on Bungie's help site seems to indicate that these bans are permanent without chance of appeal. That would be pretty harsh for gamers just trying to keep an eye on their graphics card's temperature while playing the latest heavily-demanding AAA game.
During the beta tests on PC, players brought up concerns that they were being removed from the beta for using monitoring and capture tools. A post from a Bungie employee (reproduced above) explicitly states that the removals weren't related to the software in question. More recently, David Shaw—Bungie's project lead for the PC version of Destiny 2—said on Twitter that he doubts the banned users' claims, calling them "internet BS." His response does seem to again indicate that Bungie didn't intend to hand out bans just for using common software tools, though.
Whatever the root cause for the bans might be, it seems that Bungie's anti-cheat tech could be a little trigger-happy right now. If you're planning of stepping into the shoes of one of Destiny 2's Guardians, we'd strongly recommend closing any apps not directly related to the game, at least until this controversy is cleared. I haven't had any trouble with Steelseries Engine, but maybe I'll close that too just to be safe.