Why can't viruses be killed?

Some users often report that the same virus has been detected on the hard disk for a while after antivirus software has been used, and the virus has been repeatedly killed. Why?
This is actually caused by improper processing of some super infectious viruses, such as 3783, rather than the virus being "killed ". In this case, the user should follow the following principles for anti-virus:
① Check whether anti-virus software is infected with viruses.
② Make sure that Anti-Virus is detected after the disk is started from a clean floppy disk.
③ Some machines can set the "VirusWarning" or "Systemprotect" item in CMOS and change the item to "Disable" before anti-virus ". If the virus has been infected with the Master Boot area of the hard disk, this function will protect the virus code in the master boot area. After the virus is eliminated, it will become "enable ".
④ All files and directories on the hard disk should be checked for antivirus purposes, and all files on the disk should be checked before use. Pay special attention to this because most of the anti-virus floppy disks are used by default after they are started. Most of them are only checked *. EXE ,*. COM ,*. DOC ,*. DOT and other files, but some viruses will not only infect the above files, but also infect *. dll ,*. DRV ,*. SYS ,*. INI, which may cause some infected files to be missing because they are not found.
⑤ Check whether there is a virus in the compressed file. Pay special attention to files similar to PKLIKE. EXE that can be self-decompressed.
⑥ If the above time is exhausted, the virus remains stubborn. Please upgrade anti-virus software as soon as possible.