Odd System Behaviour

My system started to slow down and would reboot during a malware scan with Windows Defender, Malwarebytes Anti-Malware. I did however get a quick scan completed with Defender.
I have since restored a system image and things seem to be ok.

Any way to make sure the culprit isn't lurking around anymore?

This got me thinking now about purchasing a full fledged internet security software.

Currently I'm using Windows Defender and scanning only with Malwarebytes and Microsoft safety scanner.
Is this enough?
Should I go out and pay $50 or so for security software??
I know this depends on many things but I would appreciate any suggestions.

James

Only you know your browsing and SW installation and usage habits, so it's difficult to answer but you can check what difference is between free and payed AVs is. You can check that by going to some AV sites and see for yourself.
Here's Avast site for instance :
AVAST 2014 | Download Free Antivirus Software for Virus Protection
There's similar stuff for all other major ones too.
If you suspect some particular threat there are some programs that deal just with them. You can find a good selection of them on sites like : MajorGeeks.com - MajorGeeks and similar ones.

I'll look into Avast.
I did install Avast, but I did so when my system was infected.
My system got much worse after installing it. I was unable to run anything form my start screen and windows couldn't find the path the user name.

Seven Forums has a thread listing various AV's along with their pros/cons

What's the Best Anti-virus? - Windows 7 Help Forums

Installing an AV after your system is compromised does no good as the virus will corrupt the AV program. Hopefully you made the system image before the malware was present. If not, you may have introduced it back into the system. Keep a close eye on your systems behavior. Other tools you can use to scan for malware:

TDSSKiller - This will run a scan for rootkits.

TDSSKiller Download

AdwCleaner

AdwCleaner Download

Note: The Microsoft Safety Scanner expires 10 days after being downloaded. To rerun a scan with the latest anti-malware definitions, download and run the Microsoft Safety Scanner again.

The Microsoft Safety Scanner is not a replacement for using an antivirus software program that provides ongoing protection.

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I would buy the Pro version of Malwarebytes if you are convinced you need to pay for security software. Run "sfc /scannow" at a command prompt to see if any errors are found. Whenever anyone tells me their system is "infected", it invariable isn't but there are usually software issues I need to address...