ClamWin is free and open source. I found it a bit quirky. But the last time I tried it was a couple of years back.
Edit: List of supported OS stops with W8.
Yes, MSE (now just Defender in Win8 & >) has done a great job for me for the past decade or more. (Before MSE there was Windows Live One Care which morphed into MSE, which morphed into Defender in Win8 & >.) It is minimally invasive and has a very small resource-consumption footprint and has caught everything my machines have encountered with the huge blessing of pretty-much no false positives (unlike I saw with MalwareBytes, which labeled orphaned registry text strings as "possible malware.") I average a definition update a day, if not more frequently, which seems to mean they're staying on top of things.
Please note that the ZDNet article linked to by Brink does not mention Windows 10. That is very important to understand.
I think at the present time it would be best to avoid all third party security software on Windows 10. You should never use such software on an OS it has not been advertised as compatible with. Nobody can honestly claim full compatibility with an OS that is in a state of active development and I am not aware of any that have made such claims. I expect that few have even seriously looked into compatibility issues at this time. The compatibility issues inherent with security software are far more serious than with most other software.
After Windows 10 has been officially released and security software advertises compatibility it can then be seriously considered.
This has been discussed in this thread:
Warning - Do NOT use norton with windows 10
Am I missing something? I thought that was to point to test all software including virus protection software, not just what Microsoft provides. In fact, Microsoft claims that the software you use on Windows 7 will work with windows 10 unless that has change as well.
Technically, Windows 10 is a virus-in-a-way because it reports back to Microsoft. So, Norton's got it right but just didn't now how to fix it correctly.
The statement by Microsoft is very broad and general in nature. It does not mean that 100% of applications that run on Windows 8 will run on Windows 10. Windows 10 obviously has made many changes from Windows 8. Microsoft has learned from long experience that even the most trivial changes can and has broken applications. That includes optimizations, code cleanup, and even bug fixes. Even popular applications from major suppliers have had such problems. And I must emphasize, the compatibility constraints for an AV product are far more stringent than for normal software. Even serious problems may be completely unnoticed by users.In fact, Microsoft claims that the software you use on Windows 7 will work with windows 10 unless that has change as well.
LMiller7 and Jeff, Thank you.
I have Avast Premium on two rigs. All others, including Win10 ones, have Defender and I'm happy with it !Using Defender myself on all computers and like it.