One more opinion. You say you got your computer last year. I'm guessing you've been running without any kind of antivirus for all this time. (Windows Defender, an antispyware, should have been turned on by default with Windows 7.) For the time being, I'd recommend using the free Microsoft Security Essentials (MSE). It's made by the same folks who make Windows 7 so there should be no compatibility issues other than you must be using genuine Windows 7. Install it, update it, then run a full scan to make sure you haven't picked up some malware since you got your computer. (MSE is a combination antivirus/antispyware so it will automatically turn off Windows Defender. This is normal and not a problem.) Virus, Spyware & Malware Protection | Microsoft Security Essentials
Once you've scanned with MSE, I'd also suggest you get the free Malwarebytes as a second tool to scan for anything MSE might have missed. (No antivirus is 100% effective 100% of the time so a second scanner is a good thing.) Again, install Malwarebytes, update it, and run the full scan. You can download Malwarebytes from CNET. Use the big gray button on the left that says Download Now (9MB). Malwarebytes Anti-Malware - Free software downloads and software reviews - CNET Downloads
The first time you run a full scan with either MSE or Malwarebytes it could take well over an hour depending on the size of your hard drive. Again, not to be concerned. When you've become familiar with antivirus programs and how they update and run, you can always experiment with other products. Hope this helps.