An unknown hacker on Friday morning infiltrated Oldsmar’s water treatment plant and ultimately made potentially dangerous changes to the chemical levels.

Pinellas County Sheriff Bob Gualtieri said at a news conference Monday there were two intrusions, hours apart.

The first one happened at 8 a.m., when a plant operator noticed someone remotely accessing the system he was monitoring, which controls chemicals and other plant operations. But he didn’t think much of it, according to the sheriff, because it was brief and his supervisors and others remotely access the system to troubleshoot problems.

Then, at around 1:30 p.m., there was another, longer intrusion – about five minutes.

According to the sheriff, the operator saw the mouse moving around as the hacker opened various software control functions.

“One of the functions opened by the person hacking into the system was one that controls the amount of sodium hydroxide in the water. The hacker changed the sodium hydroxide from about 100 parts per million to 11,100 parts per million,” Sheriff Gualtieri explaned. “This is obviously a significant and potentially dangerous increase. Sodium hydroxide, also known as lye, is a main ingredient in liquid drain cleaners. It’s also used to control water acidity and remove metals from drinking water in the water treatment plant.”

The Sheriff said the public was never in any danger, though. After increasing the chemical level, the hacker exited the system, and the plant operator immediately reduced it.

“Even if the plant operator had not quickly reversed the increased amount of sodium hydroxide, it would have taken between 24 and 36 hours for that water to hit the water supply system,” Gualtieri explained. “And there are redundancies in place where the water had been checked before it was released.”

The sheriff says the Pinellas County Sheriff’s Office was notified of the intrusion late Friday afternoon and began a criminal investigation that involves the FBI and U.S. Secret Service.

“We don’t know right now if the breach originated from inside the United States or outside the Country,” Gualtieri revealed. “We also don’t know why the Oldsmar system was targeted, and we have no knowledge of other systems being unlawfully accessed.”

As for what the city of Oldsmar is doing in response to the hack of its water treatment facility, Mayor Eric Seidel said this:

“The reality of it is, though, that the redundancies that we have in place – they work. But everybody should be on notice. We certainly feel like we’re taking a hard look at what we can upgrade and that type of thing from prevent it from happening again.”