Megabyte (voiced by the late Tony Jay) is a virus, originally operating out of the Silicon Tor in Sector 1000 and dominating most of G-Prime. Megabyte plots constantly to corrupt and control Mainframe in order to turn it into his own domain, “Megaframe”, and from there infect the Super-Computer and then take the entire Net. He is a malignant virus, with the ability and the desire to infect other programs, and commands an army of infected Binomes. Megabyte possesses great physical strength (along with vicious Wolverine-like extendable claws) and an exceedingly cunning intellect. In many ways he is a megalomaniacal dictator; his only purpose is the amassing of power and control. Megabyte has no scruples and constantly takes advantage of other characters in order to achieve his own ends, even enslaving & torturing his own sister into use as a weapon. He has a brutal, almost psychopathic nature and speaks with a deep British accent.

At the tail end of Season 2, Megabyte worked with Mainframe to defeat the Web; unfortunately, at the moment of victory he betrayed them, shot Bob into the Web, and had his ABCs obliterate the crippled CPU air force. Only 9 CPUs survived the battle intact. For the rest of Season 3 he had virtually complete air supremacy and had Mainframe’s defenders trapped in the Principal Office while he could enslave the rest of the System. He also left Enzo alive so he could launch a propaganda campaign focusing on how the Guardian was an inexperienced boy, thus demoralizing the population.

He was finally trapped, along with all of G-Prime, behind a Firewall; unfortunately, a rampaging Hexadecimal took out the Firewall, and much of G-Prime (including the Tor) and neighboring Sectors. Megabyte now needed a new base, and as the Principal Office shields were still not online (having been deactivated to provide energy for the Firewall) he was able to conquer it by force.

Mainframe became Megaframe, a decaying and devastated System that was on the verge of crashing. When Matrix and Bob returned to the System, Mainframe’s rebels were finally able to bring down the Viral forces. During the battle, Megabyte was confronted by Matrix, who was carrying his gun. Megabyte convinced Matrix to drop his weapon and fight him hand-to-hand, as the virus believed that “the boy” would be no match for him physically. However, this was proven to be false when Matrix ultimately defeated him in battle. Megabyte was enraged when Matrix spared his life, and as an act of desperation he tried to escape to the Super-Computer. However, Mouse managed to change the address of the portal Megabyte was using, and as a result he was trapped in the Web.

Megabyte survived in the Web due to sharing some of Bob’s Guardian code, and in the fourth season he became a Trojan Horse virus, gaining the ability to look and sound like any sprite or Binome he is able to steal code from. He returned from the Web in the form of Bob circa Season 4, deliberately trying to confuse everyone over who the real Bob was in order to attack his enemies emotionally – he’d switched objectives from world conquest to personal revenge. His plan worked so well he almost ended up married to Dot, until Glitch forced him back into his Viral form. Megabyte immediately fought the real Bob, but he was surprised by Bob’s power and was forced to retreat. Afterwards, Megabyte began building an army of Neo-Virals but was swiftly captured by the CPUs along with his whole horde – or so everyone thought. That Megabyte was in fact an alias, a fragile copy of himself, while the real Megabyte had infiltrated the Principal Office in the form of Frisket. He swiftly infected the War Room and had his enemies isolated throughout the building, telling them to prepare for “the Hunt”.

Both Megabyte and Hexadecimal were at one point part of the larger virus Gigabyte. It split into two effectively opposite (yet both evil) parts, Megabyte representing order and Hexadecimal representing chaos.

His name is a reference to a unit of computer memory.