The attempt on Friday was thwarted. The hackers remotely gained access to a software program, named TeamViewer, on the computer of an employee at the facility for the town of Oldsmar, near Tampa, to gain control of other systems, Sheriff Bob Gualtieri said in an interview on Monday.
"The guy was sitting there monitoring the computer as he's supposed to and all of a sudden he sees a window pop up that the computer has been accessed," Gualtieri said.
"The next thing you know someone is dragging the mouse and clicking around and opening programs and manipulating the system."
The hackers then increased the amount of sodium hydroxide, also known as lye, being distributed into the water supply. The chemical is typically used in small amounts to control the acidity of water, but at higher levels is dangerous to consume.
The plant employee alerted his employer, who called the sheriff. The water treatment facility was able to quickly reverse the command, leading to minimal impact.
Oldsmar Mayor Eric Seidel said in a press conference on Monday that the affected water treatment facility also had other controls in place that would have prevented a dangerous amount of lye from entering the water supply unnoticed.
"The amount of sodium hydroxide that got in was minimal and was reversed quickly," Gualtieri said.
The affected water treatment facility is a public utility owned by the town, he explained, which has its own internal IT team. Oldsmar is about 27km northwest of Tampa and has about 15,000 residents.
TeamViewer, which says on its website that its software has been installed on 2.5 billion devices worldwide, enables remote technical support among other applications.
The FBI and Secret Service have been called in to assist in an investigation. Gualtieri said he does not know who is responsible for the cyberattack.
"The important thing is to put everyone on notice,” he said. "This should be a wake-up call."
