What should I do after my antivirus quarantined a Trojan horse?

You shouldn't run that program since it was quarantined for being potentially harmful. Be careful when downloading stuff and stick to trusted sources.

First off, you should install a reputable antivirus program and run a full system scan to make sure everything's clean. Windows' built-in protection is just basic. If you find more issues after scanning, consider reinstalling Windows and formatting your drives to ensure you have a fresh start.

You might be dealing with tricky malware. Malware can use sophisticated tactics to get on your machine. Just be cautious, always confirm the software is legitimate and get it from trusted sites. Also, keep your antivirus updated to avoid issues in the future.

Running the program that was quarantined isn't a good idea. It was flagged for a reason, so avoid trying to download or execute it again. Instead, I'd recommend looking for safe alternatives, such as open-source software if that was what you were after.