"What did you hear about us?"
"What do you know about us?"
"What do you think we do at this company?"
I feel this question is not to quiz you about your knowledge about the company. It also doesn't test if you researched this company or not. I feel that this question is to find out what you know before they explain some things about there company. You should understand that if you are a strong candidate and you are doing well on your interview, then they will start sharing some things about the company to entice you to take the position. However, it could turn out to be a quiz so make sure you do your research before interviewing for a position.
Short Answers
"I heard that ABC Company is the leader in copy machine distribution. ABC Company is a global company in 18 different countries, and finally, it's one of the best companies to work for."
"I heard ABC Company has a great work environment and a place where strong contributors are rewarded. I want to work for a company with opportunities and I know ABC Company provides these things."
"I read on your website that ABC Company provides accounting services to small and medium size corporations. I also know ABC Company is the leader in tax services in this area. That's why I'm excited to have the opportunity to join this company."
Long Answer
"I heard a lot of good things about ABC Company. I know this company provides financial services to small and medium size corporations. Specifically, ABC Company focuses on creating automation for routine financial transactions. Besides what the company provides, I heard that the office environment is great and the employees are well taken care of."
You don't have to list everything you know... just enough to let them know that you did your homework. Also, take a little time to give the company a compliment such as the last sentence. It is a psychological tool that you should use to your advantage. This type of compliment is directed at the company and the interviewer will be happy to hear this.