On February 5, 2021, a water treatment plant employee in Oldsmar, Florida noticed his mouse cursor moving strangely on his computer screen. At first, he thought it was nothing because they use remote-access software. Later, the mouse moved again to adjust the allowable level of sodium hydroxide (a disinfectant used to clean the water). Although the intrusion only lasted between three and five minutes, it took five and a half hours for the staff to notice the change to dangerous allowable levels. The plant has since disabled its remote-access system. This breach highlights the serious impacts hackers can have on utilities and critical infrastructure, potentially harming thousands of people.