The trouble with paying for a subscription to one anti-virus corporation that then gives you Firewall, AV, Spyware and Malware protection is that they cannot possibly catch everything. It is false assurance.
Avast at least claims they offer the same program and update structure - the only difference is what features are available to the end-user. (I've found the free version to be quite comprehensive, however).
You really need to "spread the eggs between baskets" for the ultimate security, and that is best practice - remember since the baddies are always a step ahead, the anti-virus corps may not share their secrets - resulting in coverage gaps.
This PC World article illustrates the differences between the best free anti-virus (Avast) and the best paid (Norton). I still wouldn't purchase software; there really is too little difference, and I never stray onto the "bad side" of the net, and run at least weekly scans across all my machines (ClamWin is also employed, despite its miserable abilities. But who knows, maybe it will shine where others don't....). Google Chrome has saved my bacon a couple of times, as has Firefox/Pale-Moon several times.
http://www.pcworld.com/article/210589/free_versus_fee_free_and_paid_antivirus_programs_compared.html
These two articles suggest that MSE is now practically worthless as a singular defense - where before it was one of the best free solutions available.
http://www.expertreviews.co.uk/software/1303828/microsoft-security-essentials/page/0/1
http://www.pcpro.co.uk/news/securit...rity-essentials-flunks-another-antivirus-test
Judging on how poorly it did, even the "free" Avast solution mentioned in the PC World article is leaps and bounds ahead. So with Microsoft, you really do get what you don't pay for....
As for the malicious advertising, 'airliners.net' is a regularly updated and maintained website. The founder of the site was always sure to respond to information about malicious advertisements - however he was bought out years ago. The last 3-4 months the advertising has gone downhill somewhat - And I very nearly had an infected system (Where thorough scanning with Windows Defender*, Malwarebytes and Avast showed no infection).
*I understand that software might actually be practically useless now too - but its another weapon in the arsenal, so make of it what you will.