In some cases, you don't know where are the computers you have authorized and would like to deauthorize them, you can deauthorize all computers by doing the following steps:
1. Open iTune.
2. Login Apple Store using your ID
3. Click Store and then select View My Account.
2. Enter your account name and password.
3. Enter your Apple ID and password.
4. In the Account Information window, click Deauthorize All.
