Mario Alberto Simbaqueba Bonilla used a "breathtakingly simple" scheme, U.S. Attorney R. Alexander Acosta said after Wednesday's hearing. He checked into at least 25 hotels in Miami, Las Vegas and other cities in the United States and overseas and installed keystroke-tracking software in computers in the business center, the Miami Herald reported.

The software, similar to programs used by parents to track children's computer activity, allowed Bonilla to track what was done on those computers from anywhere in the world. He was able to glean information including account numbers, passwords and other personal data.

The Defense Department began an investigation in 2006 after discovering that someone had gained access to the accounts of 17 soldiers. When Bonilla was arrested in August at Miami International Airport, investigators found data from more than 600 people on his laptop.

Bonilla faces up to 10 years in prison. He allegedly was aided by his ex-wife, who remains at large.