Microsoft on Wednesday denied providing Chinese authorities with information that led to the arrest of a Chinese journalist on charges of incitement to subversion.
Reports emerged on Tuesday that journalist Li Yuanlong was charged last month for using a Hotmail account to post articles on an overseas website under a pseudonym.
"Microsoft did not assist the Chinese government in this action, nor have we shared any of this customer's personal information with the Chinese authorities," Microsoft spokeswoman Charlene Chian said in an email.
Li has been under arrest since September last year, but the news that he used a Hotmail account to post his articles came out only this week.
US internet companies, including Microsoft's MSN division, have faced criticism over their operations in China.
Earlier this year, Microsoft acknowledged censoring the blog of Zhao Jing, a Chinese journalist, at the request of Chinese authorities. As a result of that case, the company amended its policy to say it would remove blogs only after receiving a formal legal order.
Yahoo, meanwhile, was widely condemned for handing over information to Chinese authorities about two Yahoo email accounts. The information was used to jail the owners of the email accounts on charges of revealing state secrets and incitement to subversion.