SQL Injection Attack
SQL is the predominant database and database query language used today. There are known vulnerabilities with SQL which can be used to exploit a Database server into divulging Data it otherwise would not. The really dangerous point with an SQL injection attack is that unlike the methods mentioned above it is a targeted attack on a specific server. A hacker will typically use 1 type of attack and if that doesn't yeild results then they will move on to another type of attack. Sadly the internet allows hackers to share newly discovered vulnerabilities almost instantaneously. The best defence here is to keep SQL and the core operating system up to date with latest patches and fixes.