I've been running Microsoft Security Essentials (MSE) in Windows 7, and the updated MSE renamed to Windows Defender in Windows 8.x and Windows 10 since Windows 7 came out in 2009 without any problems and I recommend it with no reservations.
However, regardless the anti-malware solution you use, you should have a supplemental scanner on hand for verification just to ensure you (the user and ALWAYS weakest link in security) or your primary scanner did not let something slip by. And for that, I recommend
Malwarebytes's Anti-Malware (MBAM).
And just FTR, in the 6 years since using MSE/WD, MBAM has not found that anything did slip by.
Just keep Windows and your security updated, use a decent firewall (I use and recommend Windows Firewall), don't partake in risky behavior like illegal filesharing via P2P sites and through Torrents, don't visit illegal pornography and gambling sites, and as Russ noted, don't be "click happy" on unsolicited downloads, attachments, and links (the things you must do - or not do- regardless your security) and you will be fine.