The authorities in Florida are investigating attempts by a hacker to poison Oldsmar’s water supply, police said on Monday. The hacker remotely accessed a computer and briefly increased the amount of sodium hydroxide, also known as lye, said Pinellas County Sheriff Bob Gualtieri.

“The hacker changed the sodium hydroxide from about one hundred parts per million to 11,100 parts per million,” Gualtieri said at a press conference, explaining the increase in chemical to such a degree would have made water dangerous for consumption.

The attempts to poison the water supply were foiled after an alert supervisor, who noticed the concentration being changed on his computer, reversed it immediately after the intruder exited the system, reported the Independent. The city's water supply wasn't affected, authorities said, adding they have now disabled the system used in the attack.

“The remote access … was brief and the operator didn’t think much of it because his supervisor and others would remotely access his computer screen to monitor the system at various times,” Gualtieri said.

I will be asking the @FBI to provide all assistance necessary in investigating an attempt to poison the water supply of a #Florida city.This should be treated as a matter of national security.https://t.co/XhGNLplNpr via @vice

— Marco Rubio (@marcorubio) February 8, 2021

According to the Wall Street Journal, even if the supervisor hadn’t observed the interference and intrusion into the system, other checks already in place would have alerted operators of problems ahead of water being released to residents, the sheriff said, adding the public was never in danger.

“Water systems, like other public utility systems, are part of the nation’s critical infrastructure and can be vulnerable targets when someone desires to adversely affect public safety,” Gualtieri said.

When asked if the attempt to increase the chemical levels qualified as a bioterror attack, Gualtieri said those behind the hacking would need “sophisticated” tools to breach the system.

US Senator Marco Rubio also took note of the matter and tweeted that he would ask the FBI for all the assistance.

“I will be asking the @FBI to provide all assistance necessary in investigating an attempt to poison the water supply of a #Florida city. This should be treated as a matter of national security,” Rubio wrote.

The Federal Bureau of Investigation (FBI) and the U.S. Secret Service are also involved in the probe, police said, adding they are yet to identify any suspect or find if the breach was attempted from within the US or another country.