Far from scratching messages in Arabic on paper, Osama Bin Laden communicated with the outside world using a security-conscious mix of offline email and a large library of USB sticks, US sources have reported.

The revelations, made by an anonymous US official to the Associated Press, offer insight into why Bin Laden proved so hard to locate through his Internet activity. Lacking an Internet or phone connection at his Pakistan residence, he devised a system in which he composed messages to terrorist associates on a computer, which were then copied to a USB stick, presumably using some form of encryption.

This stick was then carried to a remote computer in an Internet cafe by a courier from where it the message was sent to its intended recipient - replies where ferried back using the same laborious but hard-to-trace method.

It’s not clear yet whether he kept individual threads on each stick, or if sticks were used randomly, but the fact that the US found a large cache of these devices during the operation in which he was killed hints at the former explanation.

Bin Laden communicated with a large number of people over time and he would have needed some way of understanding the context of his communications. That would have given a reason to keep rather than destroy each stick.

Exactly what was on the reported 100 USB sticks seized is only now trickling out as US intelligence officials pore over a hoard of data that included paper writings and computer hard drives.

USB sticks have become the high-capacity portable storage technology of choice in after Bin Laden’s New York attacks, so in one respect at least the terrorist leader who shunned modern communications has been keeping up with the latest advances.

Ironically, the same technology has given the Americans data security headaches too, which caused the US Air Force to ban their use for a second time in December 2010.