August 18, 2012: Iran is taking some advice from its ally North Korea and cutting government agencies off from the Internet. This will be done by establishing an intranet. This is an Internet that is used only within Iranian government offices and the homes of some senior officials. In North Korea the only "Internet" is a similar intranet, a private network built using Internet technology but not connected to the Internet. The few North Koreans allowed access to the Internet do so through a government approved and monitored connection. North Korea has over a decade of managing this kind of intranet.
This sort of private Internet is not unique to North Korea. Back in the 1980s, the U.S. Department of Defense (which invented the Internet) created NIPRNET. This is an unclassified network using Internet technology and contains only traffic from Department of Defense users. Later the Department of Defense created SIPRNET another intranet where everything is encrypted so you can discuss highly classified material and even transmit it freely. Some corporations have similar private intranets.
While these networks are not connected directly to the Internet, outsiders can still reach them. This is usually done via a memory stick or CD/DVD containing secret software (malware) that always searches the PC it is connected to in order to figure out what kind of network connections are available. If the malware detects what it is looking for (like the North Korean or other specific intranet), the malware starts collecting information, and secretly copying it to memory sticks or writable CDs/DVDs it can reach, so that the collected date can eventually find its way to whoever created the malware. Thus an intranet will not entirely protect you from hacking. Barring the use of memory sticks and optical media (CD/DVD) is difficult to enforce, as is keeping users from plugging an intranet PC into an Internet connection.