Thanks to everyone. Some of my contact complained to me that they got junk email (with a junk link in it) and replyed to me.
Hotmail services told me someone illegally used my hotmail account and requested me to change my password when i logged on to hotmail. I have changed my password.
I didn't open any junk email. And that day when my contacts got junk email I even didn't turn on my computer.
Thanks again.