Skype Hacked Group Chat Help?

[silvershadow]

Three other friends and I were all messaging each other over the group chat on Skype. It was 2:30 am and we were all talking about nothing of importance. The host of a Skype group chat of 3 or more people is allowed to change others messages by highlighting them and typing another thing after it is sent. One of my friends was hosting our group chat that was online and we were all talking to. He knew how to change messages and he did a few times but we all got mad at him. Suddenly someone started hacking into all four of our messages and changing them or writing stuff we never typed. I told everyone to log out and log back in. Everyone did including the host of our chat. Everyone got hacked but I was the last to get hacked and the least hacked. I was on my ipod though so it may have been more difficult to hack and change messages from there. At first we wondered if it was our friend who was hosting our chat, but he wouldn't go that far. He even promised he wasn't doing anything. Then he got hacked later also. No one knew all of our passwords and I have never told anyone my password in my life. Since everyone was getting hacked on that group chat we decided to leave and start a new chat. No one hacked us after that. Do you have any reasons why this happened? Do you know how to prevent it? Why would someone hack us? Also how did they do it?