virus thru messenger

Hello every body. It's me vaibhav here. I have one question and want to know how one person did it. I don't want to harm any body. infact still i don't have much knowledge about computer so inspite of wish i can't do it. any way, my question is that once while chatting with one on msn messenger. my chat partner started loading imvioment but insted of loading normal imviorment, he loaded virus to my set. I was surprised coz it was the the genuine trick of sending virus. well, does any body know how he performed it and why my messenger didn't load normal imviorment?? regards

vaibhav