Unprofessional, Selfish...
It was a very very bad experience at all, so that I am happy to share it for others who would like to apply for:
1. After I applied online, I had quick response for a skype interview. That was with the manager of the department and it was quick and nice at all.
2. After a couple of weeks from the interview, all of a sudden I was given a challenge to solve within the next 5 days. However, it was not a very good time for me since I had prescheduled events, so I asked for just a couple of extra days, they did not bother to give a positive or negative response.
3. I put extra effort to solve the challenge, it wasn't hard at all but a little time-consuming. The questions were ambiguous, so when I asked questions for making things clear, again, I got no response. I have solved the challenge and sent it in time with my assumptions.
4. After a month, I got a standard rejection mail with no feedback. I asked for it, but they played dead.
If you ask for a candidate to invest his/her for more than a couple of days, then you should be able to show some courtesy to spend a couple of minutes to write a response...