Tougher measures to ensure the security of personal information are needed, legal experts said, after police detained four people accused of illegally purchasing students' family details and defrauding money from their parents.

Police say the suspects called the students' parents in Shanghai, disguising themselves as doctors and teachers, and asked them to transfer money. They were captured by police in Xiamen, Fujian province, on June 6.

Police said they also seized a list that contained the names and personal information of 400 Shanghai students.

"The suspects allegedly purchased the students' information online. The data might have been sold for several transfers before they reached the suspects. Police are tracking down the source," said police spokesman Zhuang Liqiang.

More than 40 reports of such cases involving more than 1 million yuan ($163,000) were made in March and April in Shanghai, police said.

The suspects were successful because they took advantage of the parents' attitudes toward their children, experts said.

"More importantly, it was because the suspects mastered the victim's personal information, which is exploited by people commonly now as a method of obtaining money illegally," said Yi Shenghua, a lawyer on criminal cases at the Yingke Law Firm in Beijing.

Police said some companies lack a confidentiality system for personal information, and sometimes that data is intentionally leaked by employees or stolen online.

Schools denied that loopholes exist in dealing with students' data. "We keep students' information secret and destroy it when it is not used anymore," said Qu Tingting, who works at the students' affairs office of Tairi School in Shanghai's Fengxian district.

Authorities should also limit who has access to residents' information within government departments, experts said.

Current laws bar government workers or employees in the industries of finance, telecommunications, education and medical treatment from selling or providing personal information to others.

Two of the suspects, who were only identified by police as Su and Ye, are husband and wife. During the phone calls, Ye pretended to be a teacher and Su played the role of a surgeon.

Police said they found more than 10 scripts at their residence, which they used while making the phone calls.

"They made up various accidents that children suffered from, such as stomach perforation, falling from a building and being hit by a vehicle, to induce parents to transfer money to them," said Wu Yufeng, one of the police officers involved in the case from the public security bureau of Shanghai's Songjiang district.

Such frauds have happened in many places in the country.

More than 20 students' parents waited outside an operating room in the First Affiliated Hospital of Soochow University in Jiangsu province on Sept 19 after receiving calls from people claiming their children were injured.

Several parents of students at the Elementary School affiliated with Renmin University of China in Beijing rushed to a hospital on Oct 18 after receiving similar calls.