Uber’s CEO, Dara Khosrowshahi, who was installed in the top job in August, disclosed the data breach last month after learning of it himself, saying that “none of this should have happened.” Uber’s security practices are also under fire in a high-stakes legal battle with rival self-driving car company Waymo, an Alphabet subsidiary.

Uber last week said it fired its chief security officer, Joe Sullivan, over his role in the 2016 data breach, which compromised data belonging to 57 million customers.

The three managers who resigned were Pooja Ashok, chief of staff for Sullivan; Prithvi Rai, a senior security engineer; and Jeff Jones, who handled physical security, the Uber spokesperson said. Ashok and Jones will remain at the company until January to assist in transition, the spokesperson said.

A fourth individual, Uber’s head of Global Threat Operations, Mat Henley, began a three-month medical leave, said a separate source familiar with the situation.

None immediately responded to requests for comment. Emails in connection with the departures, described by the separate source, complained of emotional and physical strain from the past year.

Sullivan in August told Reuters that his security team totaled around 500 employees.

Leadership in the unit has been in turmoil since the termination last week of Sullivan and a deputy, as well as Uber’s admission that it paid $100,000 to hackers to keep secret the 2016 data breach while failing to warn customers that their phone numbers and other data had been exposed.

Multiple countries have launched investigations into the delayed disclosure.

In the Waymo case, testimony at a pretrial hearing this week focused on a former employee’s claims that Uber had a special unit within its security team that tried to obtain programming code and other trade secrets from rivals.