There are many factors that influence the risk to your organisation and they are by no means all about hackers. However, we do have to deal with hackers and have to realise that they are a fact of life that won't ever go away. So how much risk are we at from hackers?
The truth of the matter is that the risk your organisation faces from hackers is proportional to the skill of the hacker. There are many different types of hacker, from the person who downloads a free tool, through script kiddies to highly intelligent, technically skilled people who can discover and exploit any vulnerabilities you may have.
The tricky thing is to figure out who you will likely get attacked by. Many organisations have the attitude that they are not a natural target so nobody will attack them and they don't need to worry about security. Unfortunately that just isn't true. Computers are very good at doing repetitive tasks without getting bored. As a test we have standard ADSL line with a web server sitting on it, which is completely non-advertised, yet it gets attacked 4 times a day on average. The problem is that if you have simple vulnerabilities or use the same components and services as others that are targets then they could be discovered on your network and exploited by simple to use tools. The problem is that the exploits are created and distributed in freely downloadable tools for all to use.
It is relatively easy for a hacker to find and exploit your system even if you aren't an obvious target.