The U.S. Department of Defense has banned use of YouTube and MySpace, just weeks after restricting soldiers' blogs.

A military general issued a memo Friday stating that use of social networking and recreational Web sites strains network capabilities and presents operational risks. The military said it will block worldwide access to the two sites as well as 11 others.

The memo states that soldiers cannot access the sites through military networks, the only lines of communication open to many on active duty in foreign countries. They can still access the sites from their home computers.

"However, if you access such sites using your personal home computer, you should exercise caution in forwarding any links or files from these sites to DoD computers or networks," U.S. Gen. B.B. Bell explained in his widely-distributed memo from Korea. "To do so could compromise OPSEC [operational security] and create an opportunity for hacking and virus intrusion."

Bell said soldiers must always be cautious, protect sensitive unclassified information, and help preserve military communications networks. He also urged them to keep in mind that the sites pose identity theft risks as well as

The blocked sites are: Pandora, 1.fm, Live365 Internet Radio, Photobucket, hi5, Metacafe, MTV, ifilm, BlackPlanet, StupidVideos, and FileCabi.

Bell cited bandwidth as the primary reason, but no gaming sites are on the list. All of the sites do allow members to share personal information with family and friends, which, if done carelessly, can endanger soldiers and their families.

The military has always urged soldiers not to share information that can endanger them, other soldiers, or the success of military plans and activities. Last year, press reports surfaced claiming that the military was trying to restrict the content of blogs and video postings out of fear it could be perceived as anti-Arab.

Defense Department representatives in the United States and spokespeople for military operations in Iraq said then that there was no new code of conduct or orders pertaining to blogs, Web sites, and videos. Commanders in war zones did warn soldiers to make sure that the images they sent over the Internet did not provide insurgents with information about tactics, techniques or procedures.

The "Multi-National Corps Iraq's Policy #9" also states that soldier owned and maintained Web sites must be registered with the unit chain-of command. Military personnel owning Web pages, portals, or sites must provide their unit, location, the Webmaster's name, and telephone number. Commanders in Iraq said that pertains to both military and non-military sites. The military also requires soldiers posting editorial content on others' pages or sites to register the URL and make sure that prohibited information is not posted on the sites.