The main (although there are a few others) free antiviruses you can choose from are.
2.bit defender free
Avast and AVG try to bundle things, avast's bundling isn't too bad, AVG's is a bit worse (it tries to offer "performance boosting tools") but both are easy to opt out of the bundling for. Avast creates little pop-up windows in the system tray (bottom right hand corner) but these aren't too intrusive, they are mostly notices saying that avast has a sale on for it's paid products. Bit defdnder free doesn't have bundling and I don't think it has many pop-ups but it's a bit short on options and settings, although it's protection is apparently very good. Personally I use avast.
More important than which free antivirus you choose (but make sure you HAVE an antivirus, free or paid) is the other stuff you use to keep yourself secure (and exercising caution at all times):
having a second opinion scanner and an antimalware tool(malwarebytes makes a free anti-malware scanner, but it's on-demand only, the paid version has live features) is very helpful,
having an up-to-date browser with plugins set not to run without your permission is crucial(firefox is a good choice, avoiding IE is generally wise) ,
having an anti-exploit tool is very useful(malwarebytes anti-exploit is good, and there's a free version),
having a scriptblocker in your browser (The Noscript extension for firefox, also free, is an example of this, it works well alongside malwarebytes anti-exploit but because of the way it means you have to make a few extra clicks to allow certain scripts on many pages you visit it takes a little bit of getting used to) is a very good idea (alongside the anti-exploit program this makes drive-by infections almost impossible).
Scanning every file you download (with your main antivirus and with a second opinion scanner, make use of virustotal as well when the file you have downloaded is a installer for a program),
keeping windows up-to-date on it's security updates,
never running exe files you cannot be absolutely sure of the trustworthiness of,
keeping windows file explorer set to show "full file extensions even for known file types" (so you can avoid viruses hiding an exe file behind a double extension, trust-me-i'm-a-picture.jpg.exe or i-promise-i'm-only-a-screenshot.png.scr are the sort of things to avoid as they are actually both executable file types, not images),
having UAC on a high setting to give you a chance to stop exe files before they run...
and most critically making regular backups of all your files and some system images to backup your operating system (settings/programs/... a system image backs up your system state so you can return t to the time when you made the image if you ever have problems, this is quicker, easier and needs less redoing of program installations and system settings afterwards than a full reinstall of the OS) incase something does go wrong.
Edited by rp88, 08 September 2015 - 11:15 AM.
Back on this site, for a while anyway, been so busy the last year.
My systems:2 laptops, intel i3 processors, windows 8.1 installed on the hard-drive and linux mint 17.3 MATE installed to USB