No! Nothing is safe, but windows defender is definitely one of the least safe on it's own.
There are many antivirus software, pick one for yourself. Also consider changing your broswsing habits, if you're likely to get a virus it usually your fault that you have it. If you use sites that are "too good to be true" or "too good to be free" then avoid these on your normal computer. If you really need to use them, make a separate, non-admin login.
I usually use virustotal website to scan any downloaded file before opening it,and if I doubt an .exe being malicious I run it Sandboxed using Sandboxie.
I don't really know what anti-virus to pick other than Windows Defender since pretty much all of the free versions have annoying messages and/or ads.So I guess I'll have to buy a licensed one.Which one do you recommend/use?
Regards
I personally use Norton by Symantec. To be honest, they all do practically the same thing, my nortoon includes backups and a few other features though which is quite nice for ~$30 a year for 10 computers.
This might be a useful thread for you to look at:
https://bitcointalk.org/index.php?topic=4450537.msg39787162#msg39787162Remember that you also need to scan dodgy websites on virus total, not only the stuff you want to download. A malicious cookie/php code can transfer every file on your computer to a company's server without you knowing it or place a piece of tracking information in your browser or your entire computer and act as a keylogger.
Some antiviruses also, like norton, don't allow for .exe files to be run that have been used by less than 5 users in their community which does make you reconsider what you download when you run it.
If you're using a bitcoin wallet, remember to whitelist the blockchain and client itself so the AV doesn't interfere with it.
Running a sandboxing vm (I assume that's what you are referring to with sandboxie) is not a great solution. I'd suggest getting another computer, even a raspberry pi will do the trick, just to secure the stuff you want to access in sandboxed mode. Or use a different login as I suggested with non-admin privilages. Alternatively, you can make a strong 15-20 random character password and put it so that you only open it using "safe mode with networking" in windows as that will kill a lot of additional processes (don't ever use your browser in this mode other than to use sites you know are definitely safe - like ones you use to update your client).
If this answers all of your questions, you might want to lock this thread as these types tend to attract spam. 
