The Virus is a man-made virus deadly to all magical beings. Two versions of the virus exist. The original was accidentally created by the American government in an attempt to give demonic powers to soldiers. It had the side effect of transforming those infected into superpowered monsters before killing them.
The second version was created by Ramsey Tate under orders from Amanda Freeman, though he was secretly working for his father, Ambrose. This version does not have the side effects of the first and is deadly to all magical beings except those with wizard DNA.
The first version of the virus was accidentally created when the government found a wounded demon and experimented on it to create super soldiers. The virus eventually got out and infected several members of the magical community. After discovering the virus, the demon Margoyle desired to use it himself and tried to find a way around the deadly consequences. Meanwhile, the Charmed Ones searched for the origin of the virus after Billie Jenkins was infected. They used the virus on themselves and tracked down the only person who was immune, as his blood was the cure. Margoyle also tried to obtain the blood and had his demons attack. After the sisters vanquished his gang, Margoyle was able to escape with a blood sample.
A few years later, Margoyle was captured by mayor Amanda Freeman after breaking into a medical lab. The mayor ordered a team of scientists to create a new virus deadly to the magical community. She presented her work to Agent Murphy, whom she believed to be on her side. However, Murphy asked the Chosen to help destroy the virus as he didn't want good people to get infected. The Chosen found the lab and vanquished Margoyle, who was kept as a test subject. They were then confronted by the mayor and her men, though the virus was stolen by Ramsey Tate, who had been placed on the team of scientists by his father, Ambrose.