Software Threats

I am currently studying for an MSc in IT Security and only have the dissertation to complete. My topic is which software poses the greatest security threat, I will be covering the software, victims and perpetrators. The groups I have currently put the software in are malicious software (viruses, worms etc.), dual use software (forensic software, password crackers etc.), file sharing software, software flaws/bugs and poorly configured software. I would be grateful if anyone could give me any ideas, references or useful links regarding this subject, as I have stated in my proposal that security forums are a means of gaining useful information.
Information regarding any other security forums that may be useful would also be appreciated.

Thank you in advance.

 

I don't think that there is one most dangerous kind of software. A virus may be a big risk on one system, but on another it is not. So you might consider making a more explicit statement for your dissertation.
For software to be a risk, there has to be a vulnerability, either in the code (bad programming), in the config (due to bad management), or in the (mis)use (badly educated users).
So, a more dimensional statement than just which is the most riskfull, is in order. You might add a second dimension: what causes the particular risk.