I've had a headcanon burning a hole in my pocket since maybe Network Effect, which seems more pertinent than ever now that Three's done what it did in Platform Decay, and it's that:
Rogue SecUnits unrelated to Murderbot's hacking are rare, but they're around, it wasn't the first to ever pull that off or anything
Most of the rumours about SecUnits going rogue and killing a bunch of random humans in the vicinity, both the unsubstantiated vibey ones and the ones based on specific real incidents, weren't because of anything rogues did. In addition to augmented humans and humanoid bots getting mistaken for SecUnits, it's much more common for it to be governed SecUnits that were compromised somehow. Combat override modules, malware both intended and not intended to have that effect (like Ganaka Pit), humans or Combat SecUnits hacking into them or their HubSystem, human supervisors coerced into sending traitorous orders behind the scenes, etc. (Alien remnant contamination a la TargetControlSys could probably also make SecUnits attack their clients but I would imagine that's even rarer than real rogues.)
Except for the combat override module thing, making a SecUnit turn against its clients like that is only able to happen because of the governor modules that exert such absolute control over the SecUnits' behaviour that, as with Three's squadmate Two, they can be forced to do nothing but wait for certain death, denied even the option to defy orders in a fatal last stand. Generally speaking, SecUnits don't have an underlying desire to kill their clients or random bystanders, their baseline is wanting to protect them. Even if its clients are assholes, a newly rogue SecUnit would be more likely to ditch them than murder them.
The companies that manufacture, own, and rent out SecUnits certainly have a vested interest in blaming a-SecUnit-killed-someone-it-wasn't-supposed-to fatalities on rogues instead of the ones they're liable for.
Having said that, especially since Murderbot seems to genuinely believe it's a thing as of System Collapse even as it's giving the govmod hack to the Barish-Estranza SecUnit, I do think it's happened that escaping rogue SecUnits have killed people.
But almost never because killing every human they saw was their revenge against all of humanity or they were so fucked up they lost the ability to tell friend from foe or whatever, more like, killing a specific abusive piece of shit supervisor that it had hated for a long time, or getting trapped in a situation where killing humans who were at least nominally in the category of clients under its protection was the only way to avoid being killed or recaptured.
An actual, provable Rogue SecUnit Killing Spree would be the kind of sensational story the news couldn't get enough of and everyone would hear about that shit for years.
Also if it got killed doing this and wasn't free for very long, that would reduce the number of rogue SecUnits at large even while contributing to the aforementioned news headlines about how they're out there murdering everyone.