Error shows "Important Security Message: Your computer has been locked up" that am unable to close

Important Security Message: Your computer has been locked up, your computer has been locked up. Your IP address was used without your knowledge or consent to visit websites that contains identity theft virus. To unlock the computer, please call support immediately. Please do not attempt to shut down or restart your computer, doing that may lead to data loss and identity theft. The computer lock is aimed to stop illegal activity. Please call our support immediately.

with a Contact Apple Support (Toll-Free) Number ****

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