A user reports that their machine is behaving erratically and they suspect a virus might be present. Which of the following would be the BEST first step to address this issue, considering that the virus's behavior is not fully known and the need to prevent potential further system compromise?
Utilize system restore to return the machine to a previous state
Run a full system antivirus scan in normal operational mode
Boot the system into Safe Mode and perform a virus scan
Reinstall the operating system to remove the malware