Kirill Kudryavtsec/AFP via Getty Images

New Orleans city employees were instructed to shut down their computers this weekend as a precaution after an apparent cyberattack. City officials have said there's no evidence that user passwords or data was lost in the attack.

The NOLA.gov website was still down for "unplanned maintenance" Sunday, but emergency services such as 911 and the fire department are still operational, the New Orleans' Office of Homeland Security & Emergency Preparedness said. The FBI and Secret Service are assisting with the investigation, the city said.

"Out of an abundance of caution, all employees were immediately alerted to power down computers, unplug devices & disconnect from WiFi. All servers have been powered down as well," said a tweet from NOLA Ready, the city's emergency preparedness Twitter account.

#Alert: At approximately 11am today, the @CityOfNOLA detected suspicious activity on its networks that indicated a potential cyberattack. — NOLA Ready (@nolaready) December 13, 2019

It wasn't immediately clear whether this was a ransomware attack, in which malicious software locks up your files until you send hackers a ransom payment. It featured in the WannaCry attacks in May and the NotPetya attacks in 2017, both of which swept through hospitals, banks and governments in several countries.

Such an attack last month paralyzed computers and websites managed by the Louisiana state government. A ransomware attack in the neighboring state of Texas took down systems operated by 23 entities in August.

New Orleans city officials couldn't immediately reached for comment.