Introduced into the plot in The Invasion of Time, K9 Mark II first actually appear on-screen in The Ribos Operation (1978). More mobile than his predecessor, Mark II exhibited the ability to sense and warn others of danger. He travels as a companion alongside the Doctor and Romana. Around the time of Romana's regeneration (the transition from actress Mary Tamm to Lalla Ward), the K9 character was explained as suffering from "laryngitis" to accommodate Leeson's departure from the series at the start of the 1979–80 season; for this time, he was portrayed by David Brierley, until Leeson's return for the 1980–81 season. When the Doctor and Romana travel to the parallel universe of E-Space, K9 is severely damaged, in Warriors' Gate (1981). The damage was such that K9 could only function in E-Space; when Romana decided to stay and forge her own path, the Doctor gave K9 to her. The character makes subsequent appearances in remakes of the unfinished serial Shada, alongside the Eighth Doctor (Paul McGann); the 2003 Shada audio play and webcast depict K9 Mark II as having returned to Gallifrey with Romana, now Lady President of the Time Lords, where the Doctor visits them. It is not clear if either of these audio appearances are considered canonical in relation to the continuity of the TV series.
The Norton Solution most like K9 Web Protection is Norton Antivirus Plus.  Norton Antivirus Plus provides comprehensive, mutli-layered security to protect against existing and emerging malware threats.  Norton Antivirus Plus also helps protect your private and financial information when you go online.  Finally, Norton Antivirus Plus provides 2GB of cloud storage†.
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)
Whereas Sarah Jane lifted K9 Mark III into and out of her car, (TV: A Girl's Best Friend) K9 Mark IV had a "hover mode" allowing him to negotiate the stairs of the Smiths' three-story house and bi-level attic, and to enter and exit cars. (TV: The Wedding of Sarah Jane Smith, The Gift) The Eleventh Doctor implied that Mark IV was not the first to have the ability to hover. (TV: The Power of Three)
A third model, K9 Mark III was evidently constructed by the Fourth Doctor; indeed, the Eighth Doctor did not dispute the presumption that he had built this K9. (PROSE: Interference - Book Tqo) Mark III travelled with the Fourth Doctor and Adric for a time. (PROSE: Inter-Galactic Cat) Eventually, however, he was shipped in 1978 to Sarah Jane Smith at the home she had shared with her Aunt Lavinia in South Croydon during her companionship of the Third and Fourth Doctors. (TV: A Girl's Best Friend) Since parting ways with the Doctor (TV: The Hand of Fear) however, Sarah Jane had already gone away and was travelling extensively. The following year, Lavinia purchased a manor house and market garden in Moreton Harwood, Gloucester, and took the still crated K9 with her. On 18 December 1981, Sarah Jane and her foster brother Brendan Richards arrived at Lavinia's home for Christmas, but Lavinia had left early for her lecture series in the United States. Sarah Jane opened the crate and received her new companion. (TV: A Girl's Best Friend)
Serving the surrounding areas of Dallas, Frisco, Allen, Richardson, Garland, & Mesquite. Since 1993, K-9 University has delivered high-class obedience training for dogs from our two serviceable locations in Garland and Plano. Since then, we have extended our services to include boarding, grooming, and doggy daycare. Our experienced and compassionate staff will train and care for your dog as if they were our own. Speak with us about our services by calling our location in Plano at (972) 801-9090 or Garland at (972) 530-7077.
We’re immensely grateful for the loyalty of our K9 Web Protection customers.  For years, many of you have been using the award-winning K9 application to protect your computers, children, and organizations from spyware, malware, adult content and other threats and risky interactions. We’ve worked together to make the Internet a much safer place for our families and communities.
Professor Frederick Marius, who invented the first K9 in the year 5000 while working on the asteroid K4067, described him as "my best friend and constant companion." Marius had a dog on Earth, but weight requirements did not allow him to bring his real dog into space, so he built K9. (TV: The Invisible Enemy) He built K9 by using the latest technology. Marius used his own medical computer, a state-of-the-art intraresponsive brain app, protective anti-radiation cladding, probes, a laser scapel, a vision and voice box and two scanning antennas. He put these parts together and created K9. (PROSE: One Man and His Dog) According to one account, the Professor copied the remnants of one of the versions of K9 created by the Doctor and given to Sarah Jane Smith. (PROSE: Tautology)
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.
When the Tenth Doctor created K9 Mark IV to replace K9 Mark III, he added a shiny metallic blue paint job and other improvements, including an omniflexible hyperlink facility. (TV: School Reunion) Later, though, K9 reverted to his old dark green colour. (TV: Invasion of the Bane) In battling Mr Smith (and following the battle) K9 displayed a teleport facility and a laser weapon similar to the previous K9s'. (TV: The Lost Boy)
During training at Master Dog Training, a K9 officer will better understand his or her dog, and the police dog will flawlessly perform its duties. During work and practice, the handler will be able to improve his or her dog’s performance, rather than ruin it by doing something incorrectly. For a K9 Police officer, we will solve any behavior problems that the dog might be displaying, and will teach the handler how to correct these problems during work. During the K9 police test, we will be teaching how to properly pass it through all the different disciplines.
This K9 exhibited the ability to sense and warn others of danger. He was also more mobile than his predecessor, despite his problems with the swamps of Delta III, able to lift himself up on small support rods so that he could climb stairs (PROSE: The Shadow of Weng-Chiang, TV: The Power of Kroll, The Armageddon Factor) The Doctor often used a glib remark to disarm those who were surprised by K9's appearance, such as "They're all the rage in Trenton, New Jersey." (TV: The Stones of Blood)
K9 Mark I, II, III, and IV addressed whoever was directing them as "Master" or "Mistress" depending upon gender, and used the formal "affirmative" and "negative" rather than "yes" and "no". They were programmed to be both loyal and logical, with a penchant for taking orders literally, almost to a fault. Their striped collars mirrored the Fourth Doctor's trademark scarf.

On August 1, 2016, Blue Coat, Inc. (K9’s parent company) was acquired by cybersecurity leader Symantec™.  As can be imagined Blue Coat and Symantec had a handful of similar products and unfortunately, it didn’t make sense to maintain two competing products. it was decided to “end-of-life” K9 Web Protection and focus corporate and customer attention on Symantec’s line of Norton™ products.


The practical challenges of working with the K9 prop have accompanied the robotic pooch in his return to Doctor Who. Producer Russell T Davies told SFX magazine, "Yes, just as we expected, multiple takes [were required] when he bumped into a door or veered off to the left. Lis Sladen did warn us, and she was right!"[7] 2009 saw two different incarnations of K9 appear regularly in two Doctor Who spin-offs: Mark IV in the third series of BBC production The Sarah Jane Adventures, and a re-vamped Mark I in the Park Entertainment production K9.
Although the first incarnation of K9 does not appear again in televised Doctor Who media, he is the star of the 2009 K9 television series, in which he undergoes a sort of "regeneration" process from which a new, more sophisticated and futuristic K9 emerges;[1] in the first series of K9, the character is transported to London c. 2050 by Professor Gryffen (Robert Moloney). Though on regeneration the character loses his memory of his adventures with the Doctor, he assists Gryffen and several teenage companions against a dystopian regime of "The Department". The upgraded K9 has new specifications, sporting a sophisticated head-up display, the ability to fly, and more powerful laser weapons.
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