In July of last year, Song Mo, who lives in Hainan, China, suddenly received a few text messages on his cell phone at 3 am. After a while, the last text I received was about 50,000 yuan, or about 850 million won, transferred from her bank account. Mr. Song's money was withdrawn from Guangdong Province, 700 km away. Upon receiving the report, the police arrested the suspect who withdrew the money, and fortunately he was able to find 50,000 yuan. However, Mr. Song never manipulated a mobile phone or leaked personal information, but how did the crime happen?


According to Chinese police investigation, the key to the crime was the text message authentication code. Many apps in China such as Weibo and Taobao use two methods when logging in or verifying yourself. One is to input the ID and password, and the other is to receive the authentication code as a text message with the phone number entered when registering. The authentication code method is convenient because you don't need to remember your password, and it is widely used in China because it is considered safe enough to receive a code whenever you need it on your phone.

The criminals intercepted Mr. Song's verification code text message in the middle. What I used was an old phone and a 2G network. The era of 5G networks, which boasts speed and security, has begun, but where signals are poor, cell phone signals turn into 2G networks. According to Chinese experts, 2G's encryption technology is relatively simple, so it is relatively easy to decrypt.


Using these loopholes, the culprits modified the old Motorola phones that cost about 15 yuan and 2,500 won to create a kind of antenna. By connecting it to a computer and running a specific program, the police said, it can imitate the base station signal and detect nearby cell phone signals. Detected mobile phone numbers and text messages are automatically displayed on the criminals' computers. The criminals used equipment around the victim's residence to seize the text message, and a party in another area took the money.

The shooters have also been forced to switch to 2G networks using signal jammers. In addition, an authentication code was used to find personal information such as a resident number and account number required to withdraw money. It was found that after logging into various apps such as internet shopping or insurance with the verification code, the personal information entered by the user was found. To avoid suspicion, these offenses were targeted at people with heavy text messages, and the time zone was mainly at dawn.


The same thing happened in Zhengzhou, Henan Province, China last May. More than 10 residents in the same area received several texts at dawn, and over 100,000 yuan, more than 17 million won, were taken from bank accounts and Alipay. After this incident, a Chinese media outlet reported that someone has sold a detection device, and the seller said that he can detect text messages up to 5 km in length and can buy various personal information.


Chinese media have pointed out that this technique has been in constant use since 2018. Police are in the process of investigating investigations into related organizations and selling detection devices, but experts have voiced concerns over the safety of Internet privacy. This is because there is a loophole in the authentication code method that I thought would be convenient and safe, and the security of the user's personal information in the app is still poor. Experts need to urgently supplement the verification method and personal information management method using only the authentication codes of companies, and even if individuals suddenly change the mobile phone signal to 2G or the authentication text suddenly comes, the mobile phone can be switched to flight mode or powered. Advised to block it.