That's the beauty of it. Take the keystrokes example you gave. Run it. Allow it to monitor your keystrokes (by clicking "Allow" when it's doing stuff related to that). Allow it to create the file logging your keystrokes, if you want (granting it write only access when the dialog box comes up). But after you have toyed with it, you might stop it at the point when it attempts to read from that file, in order to transmit it over the internet, or whatever it's going to do with it.
Same with the screenshots. You'd allow it to do whatever you feel like, but you might stop it when it tries to actually create the screenshot file, but allow it to do everything else in order to monitor its behavior. And since it's all in real time, with dialog boxes coming up for each of its actions, it makes it quite interesting to do so.
Isn't it dangerous to assume all malicious programs will use scratch files before communicating across the network? Won't you miss programs that use purely in-memory structures?
Yes, it is. And that was just a simplified example. In practice if you were running something you were very distrustful of, you would block access to almost all of its file access. You also wouldn't leave it running for long enough to feed it enough keystrokes to get you into trouble. But even if you did, you would catch it with all the file opens (and network connection open's) before it could transmit your keystrokes and get you into trouble. In practice many file open()'s are required to perform any function.
I’ve been using Hands Off! for the functionality for the past few years, but if I had known that the functionality was based on your kernel extension, I would’ve switched away from Hands Off! in a heartbeat (I already get the firewall features of Hands Off! from Little Snitch, so the only reason I use Hands Off! is for the disk access control feature).
Out of curiosity, could you provide a link to the website advertising your kernel extension (if it still exists)? As an OS X user, I feel pretty bad that I wasn’t aware of its existence (I would’ve certainly recommended it to my friends).
Sorry for being unclear, I didn't mean to say that it was based on my kernel extension. I meant to say that we both based it off of the same kernel extension. The extension in question is called kAuthORama and is provided by Apple. (note: I'm not 100% sure that they did use that, that was just an educated guess).
Same with the screenshots. You'd allow it to do whatever you feel like, but you might stop it when it tries to actually create the screenshot file, but allow it to do everything else in order to monitor its behavior. And since it's all in real time, with dialog boxes coming up for each of its actions, it makes it quite interesting to do so.