Update Antivirus free 'Kill' Windows 7

Typically, antivirus updates needed to keep computers safe from malicious interference. But there is one update that it can 'kill' a particular computer.
This happens on AVG free antivirus update issued December 1, 2010. If the user happens to install the update, the computer will not be lit again.
As quoted from PCWorld, Friday (3/12/2010), it occurs only in updata AVG free version that runs on