My hard disk was infected by virus, I tried many antivirus and can't solve this problem, so I want to try Low Level Format software, but others said that Low Level Format is harm for hard disk, is that true? Thanks very much!

What is the problem? If you format the hard drive the virus is gone. unless its a MBR virus which since windows XP SP2 it will warn you that the mbr is infected. To remove mbr virus all you need todo is use fdisk command to erase mbr.

Otherwise you might have a hard drive problem. Scann it with hddscan for w!nd0ws with verify and see if there are bad sectors.

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Formating and Low Level formating is not a problem. There is a Rootkit that installs itself in sectors marked Bad. They must be zeroed out with a utility.

MARKED AS BAD in the filesystem is different from MARKED AS BAD BY THE HDD. In the 1st case they are REMOVED FROM USE regardless of being good or bad and you see it in the FS properties i.e. "32K in bad sectors".
If you DESTROY the FS by zerofilling the drive, the problem will be gone.

MARKED AS BAD by the HDD removes from use transparently the "bad blocks" so , unless this rootkit has low level access to error lists / use factory commands that are drive dependent, it can't access malicious code. This is VERY UNLIKE.

It is a rare rootkit- but it does exist - it takes advantage of SMART using it as part of the exploit using logical 'bad' sectors. 98% of malware will be overwritten by a clean boot to an OS and then formating- but there are several that do not.

Whats the name of the rootkit?

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Well, in this case there's little to do at home and it is easy in the lab