There's an old spy trick whereby the spy places a USB thumb drive in the parking lot of a secured building and waits for some curious person to pick it up, take it inside, and plug it in to see what's on it. And a Trojan virus shoots through the system, steals all the valuable secrets and sends them back to the clever spy.
So a found thumb drive is no treasure.
Paul Ducklin tells about an experiment at Naked Security where they bought a bunch of USB thumb drives at an auction of items lost on the city transit system in Sydney, AU.
And many of them contained malware. Quote:
Two-thirds of the keys (33) were infected. We found 62 infected files in total. The worst key contained six infected files, representing four separate items of malware.
We didn't find any OS X malware. But nine of the keys appeared to belong to Macintosh owners (or at least had been used extensively on Macs); seven of these were infected.
In other words, if you're a Windows user, don't assume that you can automatically trust everything that comes from your Apple-loving friends. And even if you're one of those Mac users who is opposed to the concept of anti-virus software, consider softening your stance as a service to the community as a whole
He made some other interesting observations. Read the article to learn about them.
With the economy being what it is, and with the popularity of those reality TV shows where people collect junk, there must be a lot of scavengers out there looking for useable throw-aways. A USB drive might not be such great find.