No, nobody can, It is impossible to make a server hacker proof, that's a fact. This is even more impossible when vulnerable freeware scripts are so commonly used (forums, bb's, guestbooks, formmails). Nevertheless, even multibillion dollar companies such as banks, government computers, credit card companies, have had server's compromised.
We consider our security hardening procedures to make your system hacker resistant. The software we install secures the system without adversely effecting or hindering the normal operations of your server.