该代码在将待删除的文件使用随机字符进行多次覆盖写操作然后再进行删除，这样数据恢复软件就只能恢复出最后一次擦写的内容，而看不到原本的明文。-The code in the file will be deleted multiple coverage using random characters and then write to delete, so that the data recovery software can recover the last time to erase the contents, not the original plaintext.