(CNN) - From the new head of al Qaeda core, Ayman al-Zawahiri, to terror propagandist Ayman al-Awlaki, using the Internet to spread the jihadist message is a tool of the trade for terrorists.
In the last six months of 2011, Google agreed to remove some 640 terrorist videos from YouTube at the request of law enforcement officials in the United Kingdom, because the videos violated the company's guidelines. The disclosure was contained in Google's biannual Transparency Report, which provides data on government requests from throughout the world to remove content from Google's YouTube and search websites.
Aaron Zelin, who started monitoring jihadist websites in 2002 in Washington, has seen a myriad of propaganda and do-it-yourself terror tricks posted in the form of videos.
The problem with trying to take some of the more egregious material off the Internet, said Zelin, is that it has a way of popping right back up again.
"In a sense, [it's] a whack-a-mole type of thing where especially activists in the West create 20 or 30 YouTube accounts, and they primarily use one and then if somebody flags, it they just take it down and go to the next one. So it's sort of this cat-and-mouse game that you're playing," said Zelin, a fellow at the Washington Institute for Near East Policy.
Brian Fishman, a counterterrorism expert at the New America Foundation, agreed. "The Internet is fundamentally an open platform. If videos are taken down, they will get re-uploaded."
Google, a parent company to YouTube, has a policy for dealing with terrorist content online.
According to a Google spokesperson, "Community Guidelines prohibit dangerous or illegal activities such as bomb making, hate speech and incitement to commit violent acts." The spokesperson talked with CNN on the condition that no name was used because the person is not authorized to speak on the record about how such material is handled.
With hundreds of videos being posted by some jihadi groups, getting a handle on all of the terrorist information that's out there can be a challenge. Google has its own defense: a built-in flagging mechanism that alerts Google moderators to take a closer look. Any YouTube subscriber, whether an individual or a government official, can select the flag button located below every video on the site.
The Google spokesperson said the flags are taken seriously and that they are constantly monitored.
"Our review teams respond to flagged videos around the clock, routinely removing material under those guidelines when content is flagged by users or other external groups," the Google spokesperson said.
Sen. Joseph Lieberman, I-Connecticut, credited Google for being responsive to concerns about what he called violent Islamist extremism online.
"These videos have played a role in the indoctrination, training, and radicalization of violent Islamist extremists, whose warped ideology advocates the killing of innocent people," Lieberman said in a statement.
But some experts say there can be hidden benefits to keeping some of this material online.
Fishman said the videos are a source of information that is important to intelligence agencies worldwide.
"One of the values of these videos being out there, we can sort of understand what our enemies are thinking about or what these kinds of folks are thinking about," Fishman said.
According to Google, the U.S. government made 1,759 requests for content to be removed from YouTube from July to December of last year. Of those requests, only one removal was in the name of national security but no details were provided on the nature of the request.
Suzanne Kelly and Pam Benson, CNN Security Blog