Trojan
Trojan
Also valid if the problem persists after attempting a Windows reinstall.
Cheap antivirus often makes things worse with a weak database and a harsh heuristic that produces false alarms 99% of the time. For better results, try a free trial of a trusted antivirus or antimalware. Alternatively, you could reset your OS drive and reinstall Windows—it’s simpler.
The Trojan has disappeared; it hasn't returned. Reinstalling and restarting Steam resolved the issue. A full system scan found no threats so far. After reinstalling, the computer runs smoother than before. Thanks for your help!
Just another update—no malware or viruses detected so far; everything is working properly now.