what operating system do you use, if you're on windows 7 or 8 just download windows defender, It's free and I've used it exclusively for ~5 years now with no problems. Windows 10 has a built in antivirus im pretty sure, but please check as I dont use Win10
Windows Defender all the way! Totally free and excellent security. Bugger paying ANYONE for this - Norton, Kaspersky etc! They're all scamming bastards! BTW, this is free with Windows 10 as well.
Make sure you uninstall Mcafee completely too as you don't want 2 AV's running, even though it's out-of-date.
As the other lads have said, Windows Defender/Microsoft Security Esssentials. i would personally install a stand alone (free) Firewall such as Comodo too, but thats my preference.