Updated

China's already repressive regime is moving to increase censorship, ordering carriers in the world's largest cell phone market to filter the billions of messages sent in the country every day.

According to the state news agency Xinhua, if the government identifies one of 13 different types of vulgar content -- including sexual content, inappropriate pictures and provocative headlines -- cell phone companies like China Mobile and China Unicorn will disable a user's text-messaging services.

Preventing the spread of pornography is a common thread in China's censorship, explains Abbe E. Foreman, a professor with the computer and information science department at Temple University's College of Science and Tech.

"They've been doing this type of censorship for some time," she said, adding that "5,000 people in China were arrested on pornography charges last year. I'm guessing they found them all through some sort of censorship program."

But many believe the government is looking for more than pornography. Kan Kaili, a professor of telecommunications at Beijing University of Posts and Telecommunication, told The New York Times that the new measures appeared broader, more intrusive and more punitive than previous limitations.

"They are doing wide-ranging checks, checking anything and everything, even if it is between a husband and wife," he told the newspaper. "I don't think people will be very happy about this."

It's unclear whether the lockdown on text messages is a new regulation, or merely the expansion of a current system that automatically monitors messages and suspends a user's account if it detects illegal content. The Wall Street Journal tried to clear up the confusion, noting that Xinhua's latest report said text messaging services would be suspended only for users who've had multiple complaints filed against them for sending pornographic mass-text messages.

China certainly has the technical ability to carry out such filtering, even on the scale of billions of text message per day, says Sal Stolfo, professor of computer science at Columbia University. With access to the network provider's infrastructure, he says, it's relatively easy to inspect messages as they flow by.

"They're undoubtedly doing keyword searches," Stolfo said, "and somebody obviously has to choose which keywords those are. But it's technically very easy to do, and scalable to billions of messages a day."

Foreman said she worries that the nature of this type of censorship makes the program easily and quickly transformable. While the government may be searching for pornographic content today, keywords are readily changed to allow the government to ferret out dissent tomorrow.

"Once you open that door, and you're looking at e-mails and text message, what's to stop someone from changing the keyword from 'sex' to 'bomb' or 'government'?" she asked. "They can use any keyword they want."

The crackdown on text messaging is just the latest attack on privacy in China, and whether the government actually implements the filters is almost irrelevant. "Just knowing it's possible reminds people who's in control, and it will have a chilling effect. People will probably avoid certain language just knowing about this," says Stolfo. "It's an intrusion of government forces into the private lives of citizens, and it's shameful."

China may be limiting texting in light of its widening spat with Google, which recently announced that it would refuse to comply with Chinese demands for censorship. Google says it is willing to leave the Chinese market entirely rather than comply.

"The challenge that the government has is to keep control. Google, an American company, is publicly challenging them. Do they have much choice? They can whimper and walk away or they can fight back," explains Stolfo.

Following Google's announcement of plans to withdraw, other companies were quick to take positions with regard to China. Microsoft notably announced that its search engine Bing, would remain in the country and would continue to comply with censorship demands.

"Microsoft will continue to engage in the Chinese market, offering Bing and other Microsoft software and services to Chinese customers," a Microsoft spokesman told FoxNews.com.

Stolfo said that was horrifying news.

"Google's strategy is don't be evil, and Microsoft came out and said, we're still evil. "