Have you recently upgraded to Maveriks?
Have you checked the Sharing pane of System Preferences?
What does your computer name show as?
If it is iMac 13,1 then you have not been compromised.

Worth a look, it might explain the email.

r



On 24 Oct 2013, at 6:02 pm, Stephen Chape <[email protected]> wrote:

> Got an email from Apple today to let me know that somebody had used my Apple 
> ID and Password to use FaceTime & iMessage on an iMac called “iMac 13,1”
> 
> Because I don’t know this iMac I have changed my Apple ID & Password.
> Is there anything else I should do ?
> 
> Regards,
> Stephen Chape
> 
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