SEATTLE — Microsoft says it will begin notifying users of its online services if they have been targets of suspected state-sponsored online attacks, joining a growing list of Internet companies stepping up their security policies with similar measures.

The company, which announced the change on Wednesday in a blog post, joins Google, Facebook and others in disclosing when users of email and other services have probably been targeted by hackers working on behalf of governments. Such attacks have increased in intensity in recent years and often involve more sophisticated, sustained forms of trickery to gain control of online accounts than those employed by ordinary digital criminals.

Reuters reported on Wednesday that Microsoft managers determined in 2012 that hackers affiliated with the Chinese government had hacked into more than a thousand Hotmail accounts, some of which belonged to leaders of China’s Tibetan and Uighur minorities.

Microsoft did not notify the targets of the hacking that the attacks came from state-sponsored sources, a decision that Reuters, citing unnamed former Microsoft employees, said was motivated by a desire to avoid inflaming Chinese government authorities.