Razvan Manole Cernaianu, known by his hacking alias of TinKode, is accused of accessing high profile computer systems without authorization, including those belonging to the Pentagon and NASA.
He often posted evidence of his activities online, the Romanian Directorate for Investigating Organized Crime and Terrorism said in a statement Tuesday.
Cernaianu, a 20 year-old IT student from Timisoara, Romania, allegedly broke into servers belonging to the U.S. Army to steal confidential information that he subsequently posted on his blog, PC Magazine reported.
He often published information online about security shortcomings in the systems he accessed, likely seeking public attention rather than financial gains, one analyst said.
"In my estimation over the last few years TinKode's motivation has been more about mischief-making than the more malicious attacks we often see, fueled by a desire for publicity via his active Twitter and Facebook accounts," Graham Cluley, senior technology consultant at security firm Sophos, said in a blog post.
"Perhaps now is a good time to remind everyone who thinks it's cool or amusing to expose an organization's weak security that hacking into a site is still a crime, regardless of what your incentive may be."
Romanian authorities said the FBI and NASA cooperated in the investigation.