Jianxin’s verification code is a means to confirm the user’s identity and prevent malicious registration. On the Internet, people often use verification codes to protect the security of their accounts. When the user enters the verification code, the system will verify the submitted information. If a mismatch is found, the user will be asked to re-enter the correct information until it matches. The purpose of this is to prevent someone from stealing your account. Verification codes can consist of letters, numbers, and special symbols. They are all randomly generated and of equal length. By permuting and combining verification codes, the system can detect a specific string. The term CAPTCHA was first coined in 2002 by Louis von Ahn of Carnegie Mellon University. Carnegie Mellon University attempted to apply for the word to become a registered trademark, but the application was denied on April 21, 2008. A commonly used CAPTCHA test is to ask the user to input text or numbers displayed on a distorted picture. The distortion is to prevent computer programs such as optical character recognition from automatically recognizing the alphanumeric characters on the picture and losing the effect. Because this test involves computers testing humans, rather than humans testing computers as in the standard Turing test, people sometimes call CAPTCHA a reverse Turing test.