China-linked hack hits tens of thousands of US Microsoft customers

A cyberattack on Microsoft Corp.’s Outlook email software is believed to have infected tens of thousands of businesses, government offices and schools in the U.S., according to people briefed on the matter.

Many of those victims of the attack, which Microsoft has said was carried out by a network of suspected Chinese hackers, appear to be small businesses and state and local governments. Estimates of total world-wide victims were approximate and ranged broadly as of Friday. Tens of thousands of customers appear to have been affected, but that number could be larger, the people said. It could be higher than 250,000, one person said.

While many of those affected likely hold little intelligence value due to the targets of the attack, it is likely to have netted high-value espionage targets as well, one of the people said.