If you play Cities: Skyline, and enjoy your healthy dose of mods to spice the game up, then you should be careful with whose mods you use. It looks like a couple of mods for the game, made by the same mod maker, have been found to be hiding malware. The mods in question are Network Extensions 3 and Harmony (redesigned).
The mod maker in question goes by the handles Holy Water and Chaos, the latter being particularly fitting. Their mods aren’t originals either, but modified versions of existing ones from other more established modders. In particular, Harmony (redesigned) was found to have an auto-updater that would allow the modder to deliver malware to devices with the mod.
Other mods by Chaos also had code that crippled the performance of mods by other makers. This indirectly caused players to use more mods made by Chaos, since they were advertised as the solution. In turn, this led to other modders looking into the issue and found the malicious code.
It’s a pretty scummy situation overall. If you still play Cities: Skyline, it’s time to revisit the mods you use, and uninstall all mods made by Chaos. You should also check your system for malware once all that is done.