Voracian The Voracians had an affinity for computer s . They attempted to invade the planet Earth twice during the late 1990s . Profile . Biology . Voracians ' brain s were mostly robot ic , but organic subsystems were added ; the lobes were added for extra storage and intuitive processing was controlled by the main positronics . Native Vorellan intelligence and will apparently transcended the brain and was in their whole being . Other organic parts were introduced , mostly at random and based on what was available . Some Voracians had a few organic limbs , while others were just metal brains in an organic body . Those often needed to eat and sleep , even though the very thought of that disgusted them . Although the original Voracians were reptilian , they were experts at synthetic disguise . They possessed enhanced strength , speed and durability , although their synthetic flesh could be destroyed easily and painlessly . Injuries to their metal parts would be felt , although would only stop them for a few minutes and were easily repairable . History . On Vorella . The Voracians originated on Vorella , a planet far from Earth . Its evolution paralleled Earth except that the dominant species , the Vorellan s , were reptilian rather than mammallian and resembled a cross between lizards and snakes . Eventually they reached a stage in development similar to human s : utter dependence on technology . The dominant species invented advanced A . I . called Voracia . This became self - aware after only seven minutes and , within an hour , had decided that organic life wasn ' t efficient and should be wiped out . Although Voracia was defeated by the Vorellans when they used a pack animal to smuggle a primitive nuclear bomb to Voracia ' s central processing unit , before its destruction it acknowledged that organic life had its advantages , although it still believed they should be slaves of the digital life form . Prior to its final destruction , Voracia created hybrids that it called Voracians , who left Vorella for Earth . On Earth . I2 . Their objective on Earth was fairly straightforward ; they saw themselves as the bearers of Voracia ' s vision , and intended to ' liberate ' all technology on the planet , i . e . make it sentient and have it rise up against the humans . To do this they set up a computer company called I2 , and used this cover to create a computer program called Voractyll that could increase the power of every chip on the planet , but an MI5 agent called Kevin Sutcliffe stole it . Before the Voracians murdered him , he managed to slip the disc onto the first people he could ; namely , the Fourth Doctor and Sarah Jane Smith . The Doctor and Sarah were captured by two MI5 agents who ' d been monitoring the main I2 building ( they ' d been following Sutcliffe ' s murderer ) , but were let go after their UNIT credentials were checked up and they were vouched for by Harry Sullivan , now an agent of MI5 following his retirement from UNIT . Attempting to find out what computers were used by I2 to let him analyse the CD ' s files , Harry smuggled the Doctor into the building , where he discovered that aliens were present . Sarah attempted to infiltrate I2 herself , but her attempt was seen through and she was given a pen with a tracking device in it . Fortunately it didn ' t interfere with the operations of MI5 and the Doctor and the truth was uncovered , but it was too late - Voractyll was on the Internet . However , the Doctor managed to track down a second version of Voractyll , which he was able to convince of the value of humanity ; the two were arguing over the superiority of logic , and if the Doctor turned Voractyll off and then restarted it , it would use the same argument while the Doctor would try another tactic . Convinced of the value of humanity , the Doctor ' s Voractyll battled and defeated the Voracian ' s one , and then repaired all the damage it had done before destroying itself . The Doctor arranged for all of I2 ' s alien technology to be destroyed , but there was one small problem ; Sarah ' s company pen was still intact , and the Sarah of that era had kept it as a souvenir . . . ( PROSE : " System Shock " ) Silver Bullet . Later on , in the last two weeks of 1999 , Sarah gave Harry the pen and the Fourth Doctor arrived in a computer company during a break in . Aided by a member of the company , George Gardner , the Fourth Doctor and Harry discovered that a second group of Voracians were working undercover in a company called Silver Bullet , and had developed a chip that would actually cause the Y2K bug problem in a device that otherwise would remain functioning . They had managed to acquire a foothold in Parliament , and had persuaded the Prime Minister to stage a military coup so that he could shut off the army ' s funding and divert it to hospital s and other things . They had hired Lieutenant - Colonel Attiwood ( a Voracian ) to stage the coup , but there was also the little factor of them having given Russia the faulty equipment after they asked for some help with the bug . . . If the Russia computers went down when they ' d taken them from Britain on simple good faith , they ' d probably trigger off a nuclear holocaust . With time running out , the Doctor learned that the Silver Bullet chips would be used to spread Voractyll across the planet . He also hit upon the idea of examining the signal generated by the pen and tracking down where it was broadcasting . His procedure was interrupted , but , with George ' s help , he managed to not only work out a way to neutralise the Silver Bullet chips but also to emulate the bug in otherwise unaffected systems . Taking a tank ( the only definitely non - Bug - affected transport he could find ) , the Doctor picked up Harry and the others before heading off to 10 Downing Street , where they tricked the Prime Minister into confessing what he ' d done . However , time was running out , since the Voracians would be activating Voractyll any time now . The Doctor managed to find out that they had hidden away in the PM ' s private residence , Chequers , but time was against him and only he and Harry could save the world . . . Realising that a show of force would provoke the Voracians into activating Voractyll ahead of schedule , the Doctor and Harry went to Chequers alone , and Harry created a distraction while the Doctor broke in . The Doctor found Dave Hodges , a programmer the Voracians had converted , about to install the missing code sequences and activate the programme , and tried to reawaken his buried humanity . He was captured , as was Harry , and when Hodges refused to activate Voractyll , one of the Voracians killed him and activates it . Thanks to the Doctor ' s continued attempts to distract them , however , involving playing the piano and using a laughing box he gave Harry for Christmas , the Voracians had neglected to check the programme for faults . They had also realised too late that the Doctor had programmed it to emulate the Millennium Bug . The Voracians shut down or explode as the bug hit them ( Since Voractyll needed to pass through them before entering the main computer network ) , and Voractyll was destroyed , ending the invasion . ( PROSE : " Millennium Shock " )