According to Sheriff Bob Gualtieri, it seems that the hacker(s) managed to gain access to TeamViewer installed on the computer of an employee working at the facility, and through the software, they attempted to try and manipulate the settings of the water supply. For those unfamiliar, TeamViewer is a software that allows someone to remotely control your computer (with permission, of course). It is typically used in technical support and remote diagnosis.
According to Gualtieri, “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. The next thing you know someone is dragging the mouse and clicking around and opening programs and manipulating the system.”
The hackers tried to increase the amount of sodium hydroxide (used to control the acidity in the water) released into the water supply, but thankfully the treatment facility was able to reverse the command with minimal impact. Oldsmar Mayor Eric Seidel later noted in a press conference that even if the hacker was successful in their initial attempt, the water treatment facility had its own controls in place to prevent dangerous levels of sodium hydroxide from entering the water supply unnoticed.