This looks like a REALLY bad false positive. It appears that AVG 7.5 for a short period of time detected user32.dll as a trojan horse. (trojan horse psw banker4). It looks as though update to the virus database VDB 270.9.0/1778 fixes the problem.
Unfortunately if you have been bitten by this, you’ll need to boot into a Rescue or Repair Console and do the following (from the Link above)…