Sina Corp (SINA.NASDAQ) warned Tuesday that a new government requirement to verify the identities of users on its popular microblog service could negatively impact its business, The Wall Street Journal reported. The Chinese internet company said it swung to a fourth-quarter profit of US$9.3 million, or 14 cents a share, compared with a year-earlier loss of US$100 million, or US$1.62 a share. Revenue rose 21% year-on-year to US$133.4 million, while the company’s gross margin narrowed to 54.5% from 57.8%. Beijing will require microblog operators to verify the real names of all users by March 16; those who are not verified will still be able to view material but not post messages. So far, more than 40% of new users have failed verification screenings, and many existing users have been unresponsive to messages from the company about having their accounts verified, said Sina CEO Charles Chao. The Weibo microblog service has reached more than 300 million users and is seeing an increase in use from mobile devices, Chao said.