My Apple account is being used by someone else

Someone in the United Arab Emirates has begun ordering apps from the app store using my account. Both my iMac and my iPhone suddenly thought I was located in the UAE. I logged out of the App Store on my phone, logged back in and it seems to be okay. I searched my iMac though and found the name and address of an unknown user in the UAE, who has purchased several security apps on my account in the last three days. My guess is she thinks this is her legitimate account, saw my recent purchasing activity and hurriedly tried to protect her own computer. My iMac displayed her name, address and phone number. Short of calling this person to straighten things out, how can I restore security on my devices?