the modification time of credit card bill making technology is divided into two parts: one is the modification of the relevant date of the year, month and day, and the other is the modification of the time stamp. Most of the bills made only modify the apparent year, month and day, ignoring the modification of hidden information, which leads to loopholes when the bills are retrieved and leads to failure in use. The credit card bill is made by modifying the time stamp. Many people don't, and the bill is very poor.