Up to 15,000 current and former Detroit employees and 300 Detroit Water and Sewerage customers may have had their information compromised in a data breach last week, the city says.
The Jan. 16 breach affected fewer than 10 employee email accounts, but some contained sensitive employee and DWSD customer data.
The city says it was "highly unlikely" that the personal data was accessed, but said it would offer free credit monitoring to the thousands who may have been affected out of an "abundance of caution."
City employees will be sent letters over the next two weeks with sign-up instructions.
Mayor Mike Duggan's office says the breach stemmed from a phishing scam. Credit monitoring will cost the city $35 per person.
Local, state and federal law enforcement agencies are investigating.