BigString just released "Self Destructing Instant Messaging," a plug-in for AIM that lets you convert an ordinary IM discussion into one where the messages literally vanish from the screen moments after they are sent.
To initiate a self-destructing thread, you have to start from AOL's IM client and install the BigString software add-on. Then, from within AIM, you get an option to "Go BigString," which if the company were not so enamored of its branding, would say instead something useful, like "launch secret IM window." At any rate, once you select this option, a browser window pops up on your computer, and the person at the other end of your chat is sent a URL to pop up a similar window. The two of you then have your IM talk in this browser-based chat. In the window, the messages vanish from the screen after a predetermined period of time (default is 10 seconds), and they cannot be copied from the screen nor even screen-grabbed before they go.
You can, of course, take a picture of the screen to record your chats, or just write things down. But there's no on-computer way to actually record a BigString IM conversation.
Oddly, the URL the product uses for its disappearing Web chats is not secure (https:), so I am not sure that chat contents cannot be intercepted en route. But at least you'll know that no records of your IM are being kept on your PC.
The tool is useful for terrorists, thieves, and child predators, not to mention teenagers, job-seekers doing their seeking from the office, paranoid government types, anyone in financial services or health care, and possibly reporters' sources--just to make their jobs a little more difficult.
Despite the serious privacy the product adds to IM, the interface is overly cutesy. I would like to see an option for a more graphically-straightforward version of the evaporating e-mail.
The company is working on a Meebo-like Web-based client that will support several IM networks, but for now, as I said, you need to use the AIM client to initiate a secure chat with the product.
The service is free, and will be supported, presumably, by disappearing ads.