Typical “you’ve been hacked” popup. Somehow unable to figure out how to post a screenshot but this call center has 2 live numbers that I know of:
1-888-531-0667
1-800-329-0785
I'm pretty sure they are also responsible for phony Microsoft support popups as well. Here's what my popup said:
APPLE SUPPORT ALERT.
Your system detected some unusual activity.
It might harm your computer data and track your financial activities.
Do not close this warning or restart your Mac
Your mac’s registration key is blocked.
Why we blocked your Mac computer?
This Mac’s registration key is illegal
This Mac is using pirated software.
This Mac is sending virus over the internet
This Mac is hacked or used from an undefined location
We block this Mac for security
Contact apple helpline to reactivate your Mac