"I have heard about you." It is a fairly common statement. Consider the scenario. On a day at work, you meet a colleague. You extend your hands for a firm handshake and introduce yourself. The other person states his name. At this point, you realize the name had cropped up in a casual or a serious conversation. You decide to share this information with the other person. After your revelation, what is the other person's reaction? Is that person surprised, puzzled or uneasy? What would have been your reaction if the roles were reversed?
Yesterday, I was in a similar situation. I met a colleague for the first time. As soon as the introductions were over, I blurted out the truth. I have heard about this person before. I carefully chose the word "blurted" for I regretted sharing the truth. The other person was visibly uncomfortable. Luckily, I didn't have to analyze his facial patterns to find out what he was thinking. He carefully framed the response. "I hope you heard good things about me." It is ingenious but pointless. Ingenious because the unprepared gives out the truth. Pointless because there aren't many unprepareds.
So what can we do in such a situation? As you may have realized, there is no ideal answer to this. One way is to acknowledge and ask what context did the other person come across you. Who was he speaking to? The other way is to acknowledge and apologize for coming across the other person for the first time. Try to find out what the other person is currently doing at work. What is past is past? There is no point in worrying what the other person has heard. You may be famous or notorious. Right now, you have to move on.