How to lock a file completely from being read

[LaDidi]

Have you remove access or DENY access to account ?
It's not the same result...

Have you tried LockFile or LockFileEx API ?
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/lockfile.asp
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/lockfileex.asp

I missinterpreted what you said last time. Now I also denied any access for any user group, but the files could still be defragmented.

The next thing I tried was the LockFile and LockFileEx APIs, but neither of the prevented the file from being defragmented, in fact you could even open the files in read mode, only trying to open the files in write mode gave a lock violation.