I quit my job after finding out they were involved in illegal practices

Hi all,

I just quit my job of 1.5 years after finding out they were involved in some very illegal trading which could definitely cause a collapse of the company if it ever came out. I didnt want to sabotage my career by being a whistle blower as I am still in my 20s and at the beginning of my career. I do not think they know I am aware of what I know but, needless to say, were not very happy with me leaving. I will probably not get a good reference from them which blows as this was my first "real" job in my field.

So, my question is what the hell do I say to future potential employers? Obviously I have to list my old company otherwise there will be a huge gap in my resume. I cant tell them the real reaso why I left nor can I bad mouth them in any way because, lets face it, no one is going to hire someone who bad mouths/shows a lack of loyalty to their last job.

Please help!