When I started my PC today, an unfamiliar Chromium-based window opened automatically. It contained pages or cards with names made up of unusual numbers and dots, but the contents were blocked by my computer's safety protections. I've never knowingly installed Chrome or visited suspicious websites, and I don't remember downloading anything malicious. The window did not appear again after I restarted, although Windows required an update before restarting. What could have caused this, and what checks should I perform to make sure my PC is safe?
3 Answers
Run a full malware scan, preferably including rootkit detection. Windows Defender’s command-line scanner can perform a deep scan from an elevated PowerShell window, and a reputable second-opinion scanner can also help. If you’re especially worried, download the scanner using a different device and transfer it with a USB drive before running it. Keep an eye on Task Manager afterward and investigate any unfamiliar processes.
Chromium and Google Chrome aren’t the same thing. Many applications use Chromium internally to display web content, so the window may have come from another installed program rather than Chrome itself. Check your installed apps and Startup Apps for anything unfamiliar, then run a thorough security scan.
A screenshot or the exact window and page names would make this much easier to identify. Since the application was closed before you could inspect it, look through installed programs, startup entries, browser-related folders, and recent Windows updates for clues. The fact that it did not return is reassuring, but it doesn’t prove what launched it.

I closed it immediately because it startled me. I’ll check whether a Chromium-based program is still installed and see if I can find the same pages or tabs again.