A hacker gained remote access to TeamViewer software on a facility employee's computer to gain the control system and sought to add a dangerous level of additive to the water supply.

According to Pinellas County Sherrif, the facility treats water for about 15,000 people in the town of Oldsmar near Tampa in the US state of Florida.

Sherrif Bob Gualtieri said in an interview that the hacker's attempt was not successful.

“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 water treatment facility was quickly able to reverse the command after the plant employee alerted his employer, who called the sheriff.

The hacker used an increased amount of Sodium Hydroxide also known as lye into the water supply. The alkaline chemical is typically used to control the acidity of the water but is dangerous when used in a high amount.

The sheriff said that the intruder was active for three to five minutes. The proper chemical mix was immediately restored by the plant operator which led to minimal effect.

No arrests have been made so far. The feds and the secret service has been called to assist in the investigation. 

Gualtieri said this should be a wake-up call against the possible cyber attack and the extent of damage it can cause.

He also said he does not know who is behind the attack.