Four young men who were accused of sending mass spam text messages were indicted on charges of illegal business operation, prosecutors in Beijing's Xicheng district said Tuesday.

It is the first illegal business operation case that was brought for sending mass spam texts, which means sending spam texts is for the first time deemed a crime, Beijing News said.

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The four men, two of whom owns an advertising company, one a tech company employee and one a street vendor who also earns money by sending spam messages, sent tens of thousands of texts of advertisements per day, including real estate, family tutors and fake invoices.

Prosecutors said the men sent more than 10 million spam texts, with revenue of hundreds of thousands of yuan and a profit margin of 20 percent, from November 2008 to early 2010, when they were busted by Xicheng police.

They admitted to police that they didn't have the license for a mass texting business, but they never thought their practice was against the law or that approval was needed.

In China, mass texting is widely used by financial institutions to send notifications to their clients or by some companies to send texts to their employees. But a lot of users don't have a license and the regulation is also a headache for China's telecom and business departments.

"The mass texting emitter can be used as a tool to commit a crime like sending fraud messages, which is hidden because it is hard for regulators to distinguish them from common texts," said Beijing-based lawyer Li Sheng.

Illegal business operation carries a maximum jail sentence of up to five years.