(CNN) - The man known as the "underwear bomber" was moved to the Supermax prison in Colorado Thursday.

Umar Farouk Abdulmutallab, 25, pleaded guilty to smuggling a bomb onboard a flight from Amsterdam to Detroit, Michigan on Christmas Day in 2009.

The device, hidden in his underwear, failed to detonate as planned.

The maximum-security prison is in Florence, about 90 miles south of Denver.

Prison officials are not saying why they moved him.

CNN