The Great Hack - Need information please

[Shockwave]

In the Ars Tech article they talk about the great hack that hit 40 or so companies. One thing the article mentions is the webserver querying the database server as an entry point for attacks. I've never heard of this, and have no idea what they mean. Can anybody recommend some good websites or books that discuss security not from the encryption standpoint, but from a firewall / server security standpoint
Thanks

 

[Finality]

Ars forums are actually very technical minded. I try to stay out of the conversations to stop myself looking like a fool