According to Newser, the move is meant to keep soldiers from seeing classified info — info any American with a computer has access to:
The Army has restricted access to the British newspaper at all of its bases nationwide, the Monterey County Herald has learned. While soldiers can visit the paper’s US site, guardiannews.com, any links pointing to the British site—including those to the NSA reporting—are blocked. A spokesman for the Army Network Enterprise Technology Command (NETCOM) confirmed that the block was on, and that it was “Armywide.”
Army Cyber Command—which NETCOM works under—blocked the site “in order to prevent an unauthorized disclosure of classified information,” explained an email sent to employees at the Presidio at Monterey base. If the classified documents the Guardian has posted wound up on an unclassified computer, the Army would have to go through a “labor intensive” process to wipe the computer, the NETCOM spokesman said, then whoever downloaded them would face disciplinary action—even though the “classified” material in this case is now public knowledge and widely available.