The secret documents included material related to Nato's ISAF peace keeping force in Afghanistan, as well as an intelligence report from a private American security company analyzing the murder of the Sri Lankan foreign minister and the attempted assassination of Lebanon's defence minister.
“We take this kind of carelessness very seriously. Its primarily a matter of security for our soldiers," said Colonel Bengt Sandström, from the Military Intelligence and Security Service (MUST).
"Its also serious from a legal perspective," he added. "Carelessness with secret matters is a crime that can result in up to 6 months in prison."
The memory stick was discovered in a public computer and turned over to Aftonbladet, which in turn returned it the Armed Forces. According to the military, the memory stick contained two secret documents, along with several other unclassified documents.
MUST has begun an analysis of the memory-stick's contents to see what other risks or damages it may have caused. In addition, MUST has asked Säpo to conduct a parallel investigation
On Friday, Colonel Sandström will meet with defence attachés from countries mentioned in documents found on the memory-stick, though the Armed Forces refused to name exactly which countries.
According to the Armed Forces rules, classified information can be loaded onto USB-memory sticks. However, secret documents should be on specific, checked-out memory sticks which are to kept under within sight or locked in a secure cabinet.