Thanks for your advice, mate! After a bit of research made in Google, I have finally found the solution. It turns out that the wallet was mining in the background after all. I had to go to the appdata directory (in Windows) and inside the Virtacoin folder, you will find the virtacoin.conf file. Edit it with a text editor and where it says gen=1, replace it with gen=0. Then open the VTA wallet, and there you go. Now it takes only 2% of CPU usage. Cheesy