Telecom frauds using personal information stolen from smartphones have been rising steadily in the world's biggest handset market, Internet firm Tencent Holdings Ltd warned on Tuesday.

The huge network of illegal mobile signal sender/blockers in big cities - they are known as pseudo base stations - are the prime reason for the sudden outbreak of tech-savvy crimes, investigators said.

More than 11 million smartphones were infected by mobile viruses sent from the pseudo base stations in the first six months of the year, according to Tencent, which is helping the police monitor online crimes.

Zhu Jinsong, head of the company's information security control unit, said the number of infections has increased rapidly since the beginning of this year.

"About 1.7 million smartphones were infected in February and the number rose to 2 million in June. That is a terrifying trend," he said.

The fake base stations allow fraudsters to send short messages using phone numbers of close friends, family members or service hotlines belonging to telecom carriers or banks. Once the user opens the links on the messages, hackers will be able to install a software on the device so that they can monitor every move the smartphone owner performs on the handset, including passwords for bank cards.

Major cities such as Beijing, Shanghai and Shenzhen in Guangdong province were the worst-hit areas for telecom frauds, experts said.

Chen Dongfang, a detective working in the anti-online fraud unit of the Beijing Municipal Public Security Bureau, said cyber fraud cases involving a phishing site jumped nearly 10 times in the first eight months of the year compared to a year earlier.

"Fraudsters hide the pseudo base stations in vans and drive them around the city. This makes it difficult to track them," Chen said.

Yang Ankang, a Shenzhen-based veteran police officer who has been working on a number of telecom frauds, said the fraudsters, mostly youngsters born after the 1990s, are building a sophisticated nationwide network.

"They find their partners online and each one of them handles different activities like sending messages, transferring money out of victims' accounts and money laundering," Yang said.

Industry regulators pledged to crack down on the illegal base stations.

The Ministry of Industry and Information Technology said it is working with telecom carriers to unearth the fraudsters.

There is no clarity on the number of victims nor the capital losses due to the scheme. Yang said a phishing site his unit had crashed in July received about 58,000 views every day.

gaoyuan@chinadaily.com.cn