Sixteen people from seven provinces have been detained following the busting of a group producing hi-tech equipment for the lucrative exam-cheating market.
Half of those detained were fresh graduates and postgraduates majoring in computer and radio technologies.
They researched and developed new technologies to avoid detection by the latest official anti-cheating equipment, according to authorities.
Police swooped on May 28, a few days before the national university entrance exam, Xinhua reported on Tuesday. They found 600 cheating devices during the raids.
'Our blocking systems are designed to jam signals above 400 megahertz,' said Ma Hongzhe , a police official in Jilin province , where the cheating devices were first discovered.
'This year they sold equipment that could send out signals below 400 megahertz.'
After metal detectors were introduced in 2006, students were caught carrying signal receivers with metal loops embedded in vests and bras, which could receive test answers transmitted by radio.
The group responded by placing receivers covered in materials that could prevent detection inside rulers, erasers or watches. In some cities authorities jam radio signals around exam halls.
The tech-savvy group also studied the law to avoid severe punishments. They did not offer test questions and answers, which could lead to a charge of illegally obtaining state secrets. They also sold parts of the cheating device separately, meaning they would avoid the charge of illegally producing and selling spy equipment.
'It is difficult dealing with some of the suspects because they are only involved in part of the industry chain,' Mr Ma said. 'We could only charge them for illegal earnings.'
The fierce competition in the university entrance exam has led to a wave of cheating and fostered a lucrative industry in recent years.
A receiver that usually cost 2,000 yuan (HK$2,250) could be sold for 18,000 yuan in Jilin in the run-up to the exam, according to Xinhua.
Authorities cracked down on cheating ahead of this year's exams, which were held on June 7-9. In Jilin, two teachers were detained on June 4 for selling 27 cheating devices for more than 400,000 yuan. A total of 34 people have been detained for trying to cheat during the exam.