This story was updated at 5:46 p.m. ET.
The lockdown at NASA's Glenn Research Center in Clevelandthis morning was caused by a glitch in an emergency telephone system, NASA hasconfirmed.
It "happened Friday when a message that was part of anagency Emergency Notification System test was inadvertently sent to an employeeat Glenn," NASA headquartersspokeswoman Katherine Trinidad told SPACE.com.
A Glenn employee received an automated phone call warningthat there was a shooter inside the building, the Associated Press reported.That call was meant for another employee, possibly at NASA's Kennedy SpaceCenter in Florida, who had the same last name, the wire reported.
What was supposed to be merely a drill turned into a lockdown,with most employees and even the local police believing there was a gunman onthe premises. Local news reported possible shots had been fired.
"We were shaking in our boots," said NASA Glennspokeswoman Katherine Martin. "All we were told was there was a situationthat involved a gun."
Local police and emergency responders arrived at the scene,while the center remained under lockdown for roughly an hour, Martin said.
"The Office of ProtectiveService officials at NASA Headquarters are conducting a review of the incidentto ensure that this does not happen again," Trinidad said.
NASA declared the facility was "all clear" atabout 10:50 a.m., and shortly after sent word that the event had just been adrill.
"We've had numerous drills but never one likethis," Martin said.
The NASA center, named after former astronautJohn Glenn, employs more than 3,400 people.
While many were traumatized by the experience, some saw thebrighter side.
"It's a good practice if it ever happens," Martinsaid.
The GlennResearch Center focuses on technology development, and is the lead formanaging development of NASA'sOrion service module and spacecraft adapter development andintegration.
- Gallery ? John Glenn in Orbit, On Shuttle Discovery
- Fuel Leak Delays Launch of Space Shuttle Discovery
- Video ? Space Shuttle Discovery: A Retrospective, Part 2, Part 3
