Hackers can gain access to your web content by inserting malicious code. Be sure that your code meets security standards.
A website can be hacked into by exploiting security flaws in the database layer of an application that lets someone pass a SQL command to the database that contains a malicious syntax.
To avoid SQL injection attacks, be sure that your webdesigner specifically includes script that filters for escape characters, deals with type handling etc. whenever access to a database is involved.