Q: having troubles with authorized computers

hey there .. when i first got my ipad i installed itunes on my computer and authorized it with the same apple id i use on my device ...... my father recently got a new iphone and wanted two install a few apps so he wanted to use my apple id ... when i installed itunes on his computer and authorized it with the same apple id , but i was shocked when it said that i have 5 computers already authorize including this one ... i don't remember authorizing except 2 ( mine and my father's ) ..... can you help me de-authorizing the other computers please ??

thanks in advance