"When I was in college I did a lot of stupid things and I don't want to make an excuse for that. Some of the things that people accuse me of are true, some of them aren't. There are pranks, IMs"

Mark Zuckerberg is acknowledging that he did some silly things while in college. He is not making any reasons for his habits, however he is also suggesting that a few of the allegations versus him might not hold true. He is most likely referring to the tricks and IMs that were sent while he remained in college. It is possible that a few of these tricks and IMs were taken out of context or exaggerated, causing incorrect accusations. He is not rejecting that he did some stupid things, however he is indicating that a few of the allegations against him may not be precise. This quote shows that Mark Zuckerberg wants to take duty for his actions, but he is likewise aware that a few of the accusations against him might not hold true.