A Californa man allegedly hacked into a number of important U.S. military and government websites including a terrorism website at West Point.

On Thursday, Billy R. Anderson, 41, of Californa was charged with three separate counts of computer fraud for obtaining unauthorized access to and committing defacements of the websites for the Combating Terrorism Center at the United States Military Academy in West Point and the Office of the New York City Comptroller.

Anderson is accused of using his specialized computer skills and knowledge to hack important U.S. military and government websites, as well as over 11,000 other websites around the world.

“Among other possible effects, website defacements can disrupt an organization’s operations and damage its credibility," Assistant Director-in-Charge William F. Sweeney Jr. said in a press release.

In October 2016, a website for the Combating Terrorism Center at West Point was defaced by Anderson using the online pseudonym “AlfabetoVirtual,” officials say.

The content of the Combating Terrorism Center website was modified to display the text “Hacked by AlfabetoVirtual.” The defacement was performed by an unauthorized administrative account that exploited a known cross-site script vulnerability, thereby enabling the hacker to bypass access controls and target an internal Combating Terrorism Center website address, authorities say.

Anderson faces up to 21 years in prison if found guilty on all counts.