Back to My Mac was a feature introduced with Mac OS X Leopard (10.5) that uses Wide-Area Bonjour to securely discover services across the Internet and automatically configure ad hoc, on-demand, point-to-point encrypted connections between computers using IPsec.
[1][2] As of October 12, 2011, Apple has included Back to My Mac in its iCloud service rather than the previously used MobileMe, thus making it free to use.
[3] On August 9, 2018, Apple updated a support document to note that Back to My Mac would not be part of the macOS Mojave (10.14) release.
[4] The support document was updated again on May 31, 2019, to indicate that Back to My Mac services would be discontinued for all other versions of macOS as of July 1, 2019.
In one instance an Apple Store employee used this technology to capture the image of a person who stole a MacBook, using the built in iSight webcam.