I agree on the Avast and Malwarebytes if you’re running MS.Have had many corporate clients lately getting a nasty bug that masquerades as an antivirus. If you’re using Norton or McCFee, do not trust the automatic updates...do it manually at least once a week.
There has been a nasty popup that claims your system is infected, and includes a dialog box. Even clicking the close (x) box on the popup loads the malware. Next thing you know you try to go to any site, either by CTRL-O or typing the URL, you get directed somewhere else, and the sites get progressively offensive. The popup continues to show up, and asks for a credit card number to “renew your coverage”, so it’s a fishing scam as well. So if a popup shows up, don’t click on anything. SHUT DOWN YOU SYSTEM IMMEDIATELY! Reboot in the safe mode, scan your system, including with Malwarebytes. As for McAfee, I have found it to be useless. I have been using Kaspersky, with updates released daily.
If it is really bad, boot in the safe mode, DOS prompt, and run Malwarebytes from the DOS prompt.