Ran some sims involving bombarding an ice-age-esque Earth while being orbited by Ganymede. I accidentally clicked "Big window" instead of "Minimize" on the Steam Chat, and then these weird glitchy bars with black-and-white footage of what I was doing in US2 kept flashing, not just in the Steam Chat window, but my whole screen. Even the Dock and Top Menu Bar were affected.
Scaring the malware out of me: