"The hacker changed the sodium hydroxide (lye) from about one hundred parts per million, to 11,100 parts per million," Gualtieri said, calling that level a "dangerous" amount.
When asked if this should be considered an attempt at bioterrorism, Gualtieri said, "What it is is someone hacked into the system not just once but twice ... opened the program and changed the levels from 100 to 11,100 parts per million with a caustic substance. So, you label it however you want, those are the facts."
According to ABC News, sodium hydroxide "is used to treat water acidity but the compound is also found in cleaning supplies such as soaps and drain cleaners." The outlet noted that "it can cause irritation, burns and other complications in larger quantities."
The hacking was discovered by a plant worker who noticed the tampering of the control panel at around 8 a.m. Friday, and discovered a second attempt at changing the lye levels was made at around 1:30 p.m. the same day.
The employee was able to quickly reverse the hacker's tampering in both instances, and officials say multiple safeguards in place at the plant that provides water to roughly 15,000 homes and businesses mean the public was not put at risk.
Gualtieri told Reuters, "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."
Law enforcement is now seeking to identify the culprit, and the FBI and Secret Service have also been looped in on the criminal investigation.
Nicole Perlroth, a reporter for The New York Times, pointed out that similar attacks on water supplies have been attempted in other countries, tweeting, "This was also an attack scenario that played out in Israel last April, when Israelis accused Iran of getting into their water treatment plant. Israel responded with a hack of Iran port."