From: Backup Software

It's now possible, in several fashions, to backup systems over a
network or even a modem, for recovery from fires and even disk
crashes.

Channel extenders, such as the CHANNELink
http://www.cnt.com/products/clnk/clnk2.htm from CNT and the Symmetrix
Remote Data Facility http://www.emc.com/symmdoc.htm, are used by some
mainframe systems to create remote copies of disks (remote mirroring)
as a disaster recovery measure. Early systems used dedicated fibre or
telephone lines and ran proprietary communications protocols. Newer
systems from CNT are capable of communicating over general-purpose
wide-area networks, thus saving the costs of the dedicated lines.

It's also possible to backup PCs over your modem in an incremental
fashion, through your ISP; one example is http://www.telebackup.com.

Two other companies that do this over the Internet (out of, I believe,
more than 30) are Connected Corp., Framingham, MA; Virtual Technology
Corp., Minneapolis, MN.