The UK Ministry of Defence has told parliament that it has lost or had stolen some 87 USB sticks holding "protectively marked" - ie classified - material since 2003. However, almost all the devices were marked at the lowest grade of classification, and even the remaining few are unlikely to have contained information of any significance.
According to a written parliamentary answer by Defence minister Bob Ainsworth on Wednesday, which can be viewed here, 81 of the devices held "Restricted" data. Restricted is a blanket classification which the MoD tends to use for almost any document it generates; marking something "Unclassified" - free for anyone to look at - runs against the Ministry's institutional culture. "Restricted" is so overused that it is meaningless, effectively the same as Unclassified (unless perhaps accompanied by an additional handling caveat indicating that there might be privacy issues, as in the case of individuals' promotion reports).
One further USB stick, lost in 2006, held "Confidential" data, the next level up. This isn't really much different from Restricted, though such documents are supposed to be more securely held and handled. You're supposed to shred Confidential hard copies rather than just chuck them in the bin, for instance. Even so, this kind of info can be freely discussed with families and even friends in many cases.
Five further sticks were marked "Secret", which is theoretically the penultimate level of UK classification. In fact, so profligate is the use of the Restricted and Confidential labels that Secret information is generally more like what you would expect Restricted to be - things you'd like to keep mainly in-house but you aren't going to make a big deal about it.
Actual important secret stuff starts to appear at the Top Secret level, but the MoD isn't admitting to having lost any of that. TS is the highest grade of protective marking, but in fact it has many subdivisions and add-ons which typically require special, extra vetting and clearances. Then there are national caveats: any TS info which isn't also marked at the very least "UK/US/AUS/CAN/NZ Eyes Only" is probably not all that exciting. You wouldn't normally let le tout NATO see anything very hot.
So, if we're to believe the MoD, they haven't really lost anything of significance on USB sticks in the last few years. However, one does note that Mr Ainsworth says "the figures... continue to be adjusted as a result of additional thefts and losses along with subsequent clarification of historic incidents"; and that most of the missing sticks were apparently stolen in just one year, 2006. This suggests that actually this information is more than a little bit incomplete.
All in all, though, the MoD has created a problem for itself here where none needed to exist. If it weren't so institutionally prone to unnecessarily marking things as secrets, it could have stood up in Parliament and said "we haven't lost any protectively marked thumb drives at all". ®