In laboratory tests, the team was able to successfully conceal firearms and plastic explosive simulants from the Rapiscan Secure 1000 scanner. The team was also able to modify the scanner operating software so it presents an “all-clear” image to the operator even when contraband was detected

via Researchers find security flaws in backscatter X-ray scanners – ScienceBlog.com.

This was demonstrated on German TV in 2009, but better late than never guys!