Avast!

Avast! Anti Virus
Avast! is a powerful Anti-Viru tool. It is widely used and a thorough piece of software. It is however quite slow, it uses up quite a lot of processor and makes everything else slow. So I'd have to say running other software and using your computer in general is not very wise as you will experience slow load times on most things

Click Start, locate Avast!
Right click and select Run as Administrator
To set up a Scheduled Scan you must click on More Detail under the Scan button on Run Full Scan
The Scheduled Scan options are at the bottom, choose what settings you prefer if you wish to set up a scheduled scan
Next click on the Maintenance tab and click Update
Now click onScan Computer and choose the Full Scan option
Once the scan has been completed, click to remove any detected threats