De-Authorise iTunes account on my 3 stolen PC's

I have had 3 PC's stolen during a break in. How can I de-authorise my account on these without access to them ?

Follow these instructions from Apples Knowledge Base:

• Click iTunes Store on the left side of iTunes.
• If you're not signed in to the store, click the Account button, then enter your account name and password.
• Click the Account button again (your Apple ID appears on the button), enter your password, and then click View Account.
• In the Account Information window, click Deauthorize All. *

Note: You may only use this feature once per year. The Deauthorize All button will not appear if you have fewer than two authorized computers. If you need assistance on using this feature, please contact iTunes Store support via email (http://www.apple.com/support/itunes/store/).

You can use the Deauthorize All button.