"How long have you been looking for a job?"
I don't know if this is legitimate question for an interviewer to ask, but it is definitely possible. I don't like the question, but at least we should think about it and prepare an answer. If you have been looking for a job for like eight months, it could sound like you are a bad candidate because nobody wants to hire you. Instead, I would take a different approach than answering honestly. If the resume shows you have been out of work for a year, then you have to explain the one year. You have two options. First, you can be honest and say you have been looking for one year, or you can think of a good excuse. It's hard to lie and sound believable so I'm going to give an honest answer. If you have a good excuse for not working for a long duration, feel free to use that as an excuse.
Short Answers
"I sent out my resumes just last week. I'm very excited to join a company where I can help out."
"I've been looking for about a month now. Because of the slow economy it's taking a little longer than I expected, but I'm confident that I can be a valuable asset to any company."
"It's been about 2 months now. I wasn't as aggressive in the beginning because I was taking some classes, but now that I'm done with class, I'm really trying now."
Long Answers
"To be honest, I've been looking for a job for quite a long time. The job market hasn't been that great and it's been a little rough. But I spent my year productively by reading up on new technologies, self studying, and trying to challenge myself with small projects. I definitely learned a lot and I'm really ready to start working again."
If you have a real excuse such as a sick mother you have to take care of, here is an example.
"I have been out of work for a year, but I have only been looking for a job for about 3 weeks now. My mother had cancer and I wanted to spend the final months with her. She passed away and I can starting work again."
I don't recommend lying for this question. It could turn bad if they find out the truth later. Telling them the truth like my first example shows honesty and shows that you tried to stay productive.