I am pretty sure that some of the wallets linked here contain a hidden CPU miner.
https://github.com/Max-Coin doesn't contain qt.
The download link download from amazonaws.com
If your CPU runs on 100% load when you have the wallet open, you probably have installed a hidden miner which works for somebody else.

First post contains a broken link for the windows wallet.

If you found a miner on your computer, I'd appreciate a little tip.  I'll add the address here bit later!