China has been using mobile apps to identify people who may be spreading Covid. The data may have been used to stop would-be protesters.

Dozens of people from across China went to Zhengzhou a few days ago to protest the freezing of their savings. When they arrived in the city, they found that the health codes on their phones were red, meaning they couldn't move freely.

Tom Zhang, the owner of a textile business in the eastern province of Zhejiang, said that this happened to him when he was on a train headed to Zhengzhou. Mr.Zhang said he was stopped by the police when he arrived in the city and told his red code indicated he was a public health risk. He said he was held in a library for 12 hours.

Mr.Zhang said that the red code was used to limit the amount of money that could be deposited. It was completely ridiculous.

Mr. Zhang was part of a group of hundreds of people who had been unable to withdraw their money from rural banks for months, and were going to lodge a complaint with the bank regulators in the province. Mr.Zhang said his account held $440,000 in savings. People from this group told The New York Times that their health codes had changed.

The red health codes were posted on Chinese social media sites by many of the petitioners. Their complaints led to a lot of questions and an unusual rebuke from commentators who asked if the local authorities had abused their power.

A former editor of the ruling Communist Party's Global Times newspaper warned that the use of the health code for purposes other than epidemic control could damage the authority of the monitoring system. On Monday, his post on Weibo became a # that was among the most searched for and drew over 260 million views.

China Comment wrote that health code can't be abused. The authorities had to explain how the codes changed and what procedures were followed. Standards should be strengthened for the use of health codes in order to guard against abuse.

A worker with the Zhengzhou government hotline told The Times that they had received a lot of complaints about the red code. The Henan Provincial Health Commission told Chinese media that it is looking into the complaints from the depositors.

The investigation into the banks could take two years according to employees from the bank regulators. Police officers from his hometown came and offered to escort him out of the country.

His health code suddenly turned green as he was about to board the plane.