With me it works perfectly, and apparently it doesn't with you.
Free alternatives are Windows Defender (comes with Windows 10, and seems to have a reasonable quality there), AVG and Avira. Be sure you download the free versions from those last 2, and not some trial version; it might be somewhat hidden on their site. For AVG it's on free.avg.com ; I didn't check Avira.
Based on several recommendations, I recently downloaded Avast Anti-virus onto my laptop. it took a day or so, but I started to get multiple BSOD's with the note: System Thread Exception Not Handled Net IO.
No data was lost, but it was very irritating. Before I came to the realization that Avast might be the culprit, I looked online for a cause. Several locations suggested my drivers might be out of date, so I updated every one. Still no change. As a matter of fact, on several occasions, the frequency of the crashes increased. I had one disastrous encounter with a program called Reimage.
I started to think about changes I had recently made and came to the conclusion that the only thing that might be causing this was the new software.
I uninstalled Avast and, Bingo! No more BSOD since I uninstalled last night.
Wondering if anyone else has had a similar experience and also would appreciate some suggestions for effective, free anti-virus software that doesn't crash your computer.