its always been true however hacks and exploiters have never focused on Open source software, mostly because there goal is to make everyones life a pain to prove the money cant buy every thing for Mr Bill Gates, and even some have been known to crack windows just to try and get a high paid job at microsoft.

If you look at linux for example, if some of these intelligent people really focused there efforts to crack and find holes in linux it would be on its knee's in no time because there isnt any financial backing to solve the issues quickly.

I know people that have found open holes in there own linux operating system but wasn't too worried because they knew that hardly anyone would look for it.