You wouldn't put your personal information or account numbers on a billboard, where anyone or everyone could read it.

But there are people who thoughtlessly link their computers to peer-to-peer (P2P) file sharing networks. Historically, the end result is sometimes equivalent to a erecting a privacy-destroying billboard.  Of course, people don't intentionally trade their identities and their financial well-being for the privilege of downloading some free music files. What happens instead is that they connect to a P2P network and neglect to ensure that only the contents of their public folder is available to other users on the network.

Consequently, the entire contents of their computer become fair game.

There is a lot of hype about this problem 2 years ago, and little since. But the problem has not gone away, and the files that have escaped remain at large and continue to be potential sources of mischief. The most recent horror tale was a complaint that information about the avionics of Marine One had been located on a server in Iran. Marine One, of course, is the helicopter that the president uses to get from the White House to the airport or to Camp David. The Marines are famous for using three helicopters on all presidential trips, with two of them serving as decoys. The findings in Iran indicate there are good reasons for this practice.

Other recent P2P-related horror tales include the discovery of more than 150,000 tax returns, 25,800 student loan applications, and nearly 626,000 credit reports on a P2P network. Last year an employee of an investment firm ended up exposing information on 2,000 clients through a P2P network. The victims included Supreme Court Justice Stephen Breyer.

A study published this January also demonstrated that there is significant hemorrhaging of private health care information through P2P networks. Examples include a long document containing Social Security numbers and other personal information on 9,000 patients of a medical testing laboratory. Another spreadsheet had extensive information on 20,000 different people.  Two years ago a congressional committee heard that millions of classified or sensitive documents were floating around in P2P hyperspace. Classified documents included information on the Pentagon's backbone network, including IP addresses and password change scripts; information on ways to defeat improvised explosive devices in Iraq; and information on the security audits of government bureaus. Sensitive information included numerous financial documents, unreleased press announcements, and business plans.

Encrypting files would, of course, reduce the impact of a P2P leak, since the files would be useless to outsiders. But avoiding P2P entirely would seem to be a better policy, especially as such networks are notorious sources of malware infections.  Over the centuries, we have learned the hard way to keep our water lines and our sewer lines strictly separate. As any plumber can tell you, the reason the faucet for your bathtub is located on the wall above the tub is so that it cannot come into contact with whatever water is in the tub. This avoids the faint possibility that it could suck your bathwater back into the municipal water pipes.   It looks like we'll have to develop a similar system for data, with a carefully monitored system for sensitive data that is never allowed to come into contact with the public "sewer" data. But until a publicly engineered solution becomes available, you are on your own.