Gov. Tim Walz of Minnesota on Tuesday activated the state National Guard to help officials in St. Paul, the capital, respond to a complex cyberattack that was first detected on Friday.
Mayor Melvin Carter of St. Paul said the city had shut down the bulk of its computer systems as a defensive measure as state and federal investigators tackled what he called “a deliberate, coordinated digital attack, carried out by a sophisticated external actor.”
Mr. Carter said that the F.B.I. and several state agencies were helping assess who was behind the attack. He declined to say whether ransom had been demanded or whether there was any evidence suggesting a foreign government was behind the attack.
City officials said they have yet to ascertain whether sensitive data had been stolen.
Emergency services, including police response systems, were not crippled by the attack, the city said in a statement. The shutdown meant that city employees did not have access to the internet in municipal buildings, and that routine services such as library loans and online payment systems were inaccessible.
Large and small cities across the United States, along with school systems and hospitals, have been targeted in cyberattacks in recent years. Such attacks are often carried out by individuals who compromise networks and encrypt data, then demand ransom payments in order to restore access.
Attackers sometimes steal sensitive data — such as credit card information — that they can later sell online.
St. Paul officials said they detected unusual activity on their network Friday morning and eventually realized the city’s networks had been breached. Deeming it a serious attack, they sought help from the governor and federal law enforcement agencies as well as cybersecurity companies.
Mr. Walz issued an executive order on Tuesday directing the National Guard to assign military computer experts to assist officials in St. Paul. In the order, Mr. Walz said that “the scale and complexity of this incident exceeded both internal and commercial response capabilities.”
Ransomware attacks have become a growing menace for municipal governments. One that targeted Atlanta in 2018 resulted in losses worth millions of dollars, according to federal prosecutors who charged two Iranian men in that case.
In recent weeks, cyberattacks have crippled municipal networks in Texas, Oklahoma and Puerto Rico.
In late June, the U.S. Cybersecurity and Infrastructure Security Agency issued a statement urging officials who control sensitive computer systems to “to stay vigilant to Iranian-affiliated cyber actors that may target U.S. devices and networks.”