At first I was a little reluctant to post this, but I am sure the bad guys know this trick already.
If you have a genie intellicode garage opener, never leave your garage open and unattended.
All someone has to do is, while standing under the motor, look up and see the learn button between the motor case and light unit.
It only takes a few seconds to reach up with any thin metal thing such as a nail file or metal ruler and press that button.
Once the red light starts flashing, two presses of the remote control button will add that remote to the system.
The perp can return at any time and have full access to the garage and consequently, most houses as well.
Pressing and holding the button for 10 seconds will reset the remotes, and they must be added back individually to work.
This would be a good procedure to do once in a while, especially after non-residents had been in the garage.
The entire intellicode manual is available online for those who have lost your copy.
http://www.geniecompany.com/GenieCompany.aspx?cid=322