I've moved this provisionally to VirusScan for better support.
This is a fully updated Windows 7 SP1 with IE10 (whether you use it or not - McAfee does) installed I assume?
By "free version" can you clarify exactly what that software is called and where it is obtained from?
I'm running McAgee Security Scan plus. I'm sure it's a free version I obtained online from the mcafee site (some time ago). I'm using firefox 22.
Security Scan Plus is in no way a proper anti-virus program. It's a small, lightweight, fast program that really only checks for certain malware in memory, plus your browser cache and history for suspect sites. It's a marketing tool - it looks to see what McAfee components you've got installed - hence the "Go-Buy" messages. I don't say it's not got its uses, but I wouldn't rely on it to do very much.
Yes, as Hayton says, it's not an antivirus programme. It installs along with some other brands' software optionally when you update or install Adobe products, amongst others. You have to keep alert when installing or updating anything these days, otherwise you will get these extra things that you most likely don't need or want.
The software can be uninstalled easily via Control Panel > Programs > Uninstall a Program.
The only free full-featured antivirus from McAfee are those that come from various Internet Service Providers and some PC makers.