Scott Lang, one of the chief engineers at Vistacorp, finished one of the routine updatings to the security systems of the building with his partner Bryan, having implementing a Qubit Defense Matrix capable of encrypting itself every 1.5 seconds.
Lang was angrily called by Geoff Zorick, CEO of Vistacorp, though Lang was oblivious to his calling, as Zorick was apparently calling for someone named "Chang". Zorick demanded to know if Lang was the one that updated the payment systems. Lang had discovered what appeared to be a mistake in the systems, that made the company overcharge customers in their transactions; so believing it was a clear error in the coding, he easily fixed it.
Zorick angrily asked who told him to fix it, and as Lang explained he did it for himself as he felt it was a clear error. Zorick ordered him to change it back immediately. Lang was stunned for the demand, believing that doing something like that was illegal. Zorick threatened Lang, telling him to stick to his pay grade and do his job, as Lang was not a member of the accounts team. As Zorick left, Bryan asked Lang what was he going to do, and Lang headed to the Human Resources section.
Due to trying to do the right thing, Lang was fired from Vistacorp, and accused of trying to extort the company.
Scott Lang broke into the Vistacorp Headquarters in order to get revenge from the whole situation that got him fired. He managed to cut the fence and enter the building while reciting the steps into a successful break-in: To know the location, to know the way around security, and to be awesome.
Lang managed to avoid being caught by security guards or cameras due to his knowledge of the security system, and entered the mainframe of the building, successfully hacking into the Qubit Defense Matrix that he installed prior to his firing. Lang entered into the accounts of the company, and returned the money that it had been illegally charging from their customers to their legitimate owners.