Hehe, this is fun.
Ok, first of all you need WINDOWS XP.
Open notepad.
And type in this:
lol = msgbox("This is windows. You have got a very bad virus, and we cannot remove it. Your computer shall shut down after you close this, but if you send all your money to microsoft and praise bill gates as your god, we will save you.",16,"Error")
This is windows. You have got a very bad virus, and we cannot remove it. Your computer shall shut down after you close this, but if you send all your money to microsoft and praise bill gates as your god, we will save you., will appear when you save.
Save it as any name, but it has to end with .vbs.
Now, when you click open, this will appear!
If you want to create your own message, Just replace the text.

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Simple as that, trick your friends!

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Oh, and another thing.
To do like 5 at a time, just copy and paste it below it.
Enjoy!
~^_^~