New update in my computer everytime i use the computer?

hi my computer has windows vista and from a days before to now when i turn the computer on and use it for a while and when i am going to turn it off there would always appear the icon that says that there is a new update and of course i let the computer update and it turns off actomatically and the same time would happen the nex time/.... does anybody have an idea of what could be wrong... please help