You have some malware which is creating the new user "Piress".
First, remove the user account - how to do this :
Then search the whole file system for a file with the name "CNA12.DLL" and delete any files you find with that name. The file should only be present if you have MySql installed, so let us know if that file is found.
Use CCleaner to clean thoroughly all temp files and unwanted files from your user account(s) and from your browser(s).
Go into each browser and remove any toolbars that you find there. Let us know which ones you remove.
If you have Java, Flash, or Adobe Reader installed, update them now.
Finally, run McAfee's GetSusp - read the "How to .." before you run it. This should isolate any suspicious files : tell us what it reports.
The Piress New User problem is not a new one and McAfee is detecting something. What is the name of the file(s) it is placing into quarantine?