More than 200 million mobile phone users in China were spammed with unwanted text-message ads in a recent "spam attack," the BBC reports.

Chinese authorities are investigating the widespread text attack that hit customers of China Mobile and China Unicom. China Mobile, which has already made public apologies for allowing mobile spam, has said it will put measures in place to block messages from seven online ad agencies, the BBC said, citing reports from China's Xinhua state-run news agency.

Both China Mobile and China Unicom have reportedly set up hotlines for customer complaints. The article doesn't say if consumers can text their complaints to the hotlines, though.