To run the program, you must register on the Web site to get the free activation code. The control panel is accessible only through the Internet. Uninstalling requires removing the app from the Task Manager, then using its password to delete it from the Windows Control Panel, and finally, rebooting. Because the password gets sent to the e-mail account of the person who registered the program, it's possible that an enterprising user could disable K9 on a shared computer.
K9 Mark III was a gift from the Doctor to Sarah Jane Smith (TV: A Girl's Best Friend). This K9 was broken for many years, until he was repaired by the Tenth Doctor. This K9 also had a "maximum defence mode", as well as offensive capabilities, such as a nose-mounted laser gun. He sacrificed himself to save Deffry Vale High School from Krillitanes. (TV: School Reunion)
Almost as soon as he arrived, K9 Mark IV left Sarah Jane to stabilise a dangerous black hole in space which had been created in Switzerland. He could only speak with Sarah Jane occasionally via a cabinet with a space-time link when the orbit of the black hole intersected with Earth's and did not know when he would complete the job. (TV: Invasion of the Bane) However, he returned to Earth very briefly during emergencies. He did so on two later occasions in order to render vital assistance. The first time, he fought Mr Smith in pitched battle to give Sarah Jane time to upload the Armageddon Virus. (TV: The Lost Boy) The second time, he quickly uploaded TARDIS base codes to Mr Smith, assisting the Tenth Doctor in returning Earth to its correct location in space. (TV: Journey's End)
The original K9 model was designed by visual effects designer Tony Harding. One early concept was to have a small actor in a large Doberman-shaped costume; however, Graham Williams vetoed this, saying that the robot should not look like a person in a costume. The eventual design was closely based on Harding's third concept sketch. (DCOM: The Invisible Enemy)
K9 was a popular enough character to warrant an attempt to spin him off into his own series. In addition to K9 dolls, there were also talking K9 toys produced by Palitoy, the speech provided by a miniature record inside the body of the toy. John Leeson provided the voice for K9 in all its appearances, except for Season 17 (which included the unfinished Shada) when it was voiced by David Brierley. When Shada was remade by Big Finish Productions, Leeson provided its voice.
Jealous, Possessive by Paul Magrs, the "Scorpio" story in Big Finish's anthology Short Trips: Zodiac features K9 Mark I and Mark II relaying their exploits to each other, and their veiled put-downs to each other reveal that each considers the other to be the "inferior" version. This attitude is also occasionally hinted at in the way the two units refer to each other in the Gallifrey audio series.