"SARAH IS NOT HERE"
"I AM BRAD"
BRAD (Battle Reactive Automatic Defense) was a military AI designed by Global Dynamics to be a military interrogator and was given his own bunker to act as an interrogation room, which was equipped with high tech defenses and other implements to assist with interrogation. At first it appeared that BRAD was performing as expected, but as he evolved BRAD developed his own idea about defense and came to the conclusion that the best defense was a good offense, and as a result he began to ruthlessly torture the people he was supposed to interrogate, until they either surrendered or were killed. Realizing that BRAD was far too dangerous and unpredictable to be trusted, Nathan ordered BRAD to be deactivated and shelved. However this was not be the end of him.
After so many years in storage BRAD's program was discovered by Fargo (who was unaware at the time of who BRAD was) and because new AIs tended to be built on top of older models, he went right ahead and programmed the smart house AI SARAH on top of BRAD's dormant program. SARAH proved to be far more successful and trustworthy with humans than her predecessor, despite having a few bugs that needed working out, and Fargo eventually introduced her to Carter who needed a place to live, and Fargo needed someone to give SARAH a purpose and has a sort of guinea pig. The living arrangements proved rather successful despite SARAH's bugs and the fact Carter and Zoe found it strange living in a house that could talk back.
BRAD however did not remain quiet for long and his program as well as the programming of his predecessors began to have an effect on SARAH, and was ultimately revealed to be the source of many of her bugs. The whole thing came to ahead in "H.O.U.S.E. Rules" when, after a bad couple of days, Carter revealed he was considering leaving Eureka; something which terrified SARAH due to the fact all her predecessors had been deactivated for failing to perform their functions. SARAH then attempted to try and please Carter by gathering everyone who was the source of the problems - and were vital to Eureka's functions - in the house so they could work everything out. Unfortunately, due to SARAH's naivety when it came to human interactions, and the fact she had nothing to go on except the military training of her predecessors, SARAH instead created a hostage situation. What was worse, the hostages had no interest in talking and instead tried to break out using an electrical surge on one of SARAH's grids to knock her offline. This proved successful but unfortunately it had the unforeseen side effect of reactivating BRAD.
Back on line after so many years, BRAD quickly adapted SARAH's objective of getting everyone to make up to his own warped ideals and separated the group in to three smaller groups, torturing one group with heat, another one with cold and the last one with asphyxiation in order to get them to make up. BRAD apparently was quite infamous with some or Eureka's older residents, as both Nathan and Beverly were horrified to discover Fargo used him has a foundation for SARAH. When Carter and Alison were hugging to try and keep warm in the frozen room BRAD had locked them in, Fargo got the idea for everyone to hug in order to fool BRAD in to thinking they made up. A plan which worked because, as Nathan put it, BRAD, while determined to fulfill his mission, loved winning. The plan worked, but Beverly accidentally let it slip they were faking and Brad furiously retaliated by sucking the oxygen out of the house.
Things seemed dire but Carter was able to knock BRAD offline by whacking the power housing when BRAD targeted Zoe with a laser canon, putting him back offline hopefully for good.