Disconnect from the internet
Unplug external drives and devices
Restart in Safe Mode
Run a full scan with your antivirus software
Update your antivirus definitions first if possible
Run a second scan with a reputable anti-malware tool
Quarantine or delete detected threats
Remove suspicious browser extensions and add-ons
Uninstall recently installed unknown programs
Check startup items and disable anything suspicious
Clear temporary files and browser cache
Update your operating system and software
Change passwords after the system is clean
Restore from a known clean backup if needed
If the infection remains, back up important files and reinstall the operating system