Bruce Schneier, one of the sharpest people in the computer security world, has a great piece about why he leaves his home wireless network open
for anyone to use. When I wrote something similar a couple of years ago, I caught a lot of flack
from people who said that I was opening myself up to security risks, either from people downloading child pornography with my connection or from people hacking into my home computers and stealing my data. But as Schneier points out, neither of these risks is unique to your home wireless network. Like Schneier, I've got several restaurants and coffee shops within walking distance of my apartment that offer free wi-fi access. While it's not impossible that somebody would park their car out in front of my street and use my Internet connection to do something illegal, it seems more likely that they'd do so over a cup of coffee in one of the nearby coffee shops, where they wouldn't evoke suspicion. Moreover, I have a laptop and I visit coffee shops and other locations with open wi-fi connections all the time. If my laptop has security vulnerabilities, I should be a lot more worried about getting cracked on those networks (which make it easy to target a bunch of people at once) than that I'll have the bad luck of living next to a cracker. I need to keep my laptop properly locked down in any event. Once I've done that, an open wi-fi network is a fairly minor risk. Finally, Schneier closes by pointing out that security is a trade-off. If perfect security is your standard, you shouldn't connect to the Internet at all, because there's always a risk of a security breach. Given that we're willing to accept some level of risk if we have a good reason, the question we should be asking is about the relative risks of different activities. The risk of leaving your wireless network open isn't zero, but it's probably small.
Now, I should point out that all of this assumes that you're a reasonably technically savvy individual with an understanding of basic security concepts: that you know how to update your operating system on a regular basis and that you've set the administrative password on your access point to a non-default value. If you're a complete networking neophyte (not that many of those probably read Techdirt), you should probably get some advice from someone more technically savvy about good Internet security practices. Actually, you should do that whether or not you choose to open your wireless network. But on the list of potential network security threats, an open wi-fi network is probably pretty low on the list.