As a follow up question of this I need to figure out a clever way to describe my situation during future job interviews. The summary of the situation: I was working for a start-up as a software developer and one day I got a task that I found unethical. I rejected the task and asked for a new one. That triggered a conversation with my boss and during this conversation I learned that the company relies on similar practices and if I want to keep the job, I need to accept them. I decided to say no so my employment will soon be history. My question is how to present this situation to my prospective employers without revealing too much about my former employer? (On personal level we agreed to part as friends, I believe it is not my task to morally judge them, I just don't want to be part of it.)
One more important thing: the whole thing happened during my probationary period and I spent 4.5 months working for this start-up. (Probationary periods are ridiculously long in this country.)
Update: please see my own answer below.