Review on Improve your iMac Security with the Kensington SafeDome Secure Lock (K64962US) by Hunter Schneider

The previous generation, which used bits left in the Kensington slot on the back of the display, was a total waste - if they were attached to the lock itself, they would just slide out. While a little tricky to set up (three hands can be used), it's simple, effective, and locks the iMac securely in place. An added benefit of the hemispherical dome design is that 90% of the lock is impervious to hackers.