Interview with an Adware Author
IE has a mechanism called a Browser Helper Object (BHO) which is basically a gob of executable code that gets informed of web requests as they’re going. It runs in the actual browser process, which means it can do anything the browser can do– which means basically anything. We would have a Browser Helper Object that actually served the ads…We then made a bootstrapper, which was a tiny tiny piece of code written in Assembler which would decrypt the executable in memory, and then just run it. At the same time, we also made a virtual process executable. I’ve never heard of anybody else doing this before. Windows has this thing called Create Remote Thread. Basically, the semantics of Create Remote Thread are: You’re a process, I’m a different process. I call you and say “Hey! I have this bit of code. I’d really like it if you’d run this.” You’d say, “Sure,” because you’re a Windows process– you’re all hippie-like and free love. Windows processes, by the way, are insanely promiscuous. So! We would call a bunch of processes, hand them all a gob of code, and they would all run it. Each process would all know about two of the other ones. This allowed them to set up a ring … mutual support, right? So we’ve progressed now from having just a Registry key entry, to having an executable, to having a randomly-named executable, to having an executable which is shuffled around a little bit on each machine, to one that’s encrypted– really more just obfuscated– to an executable that doesn’t even run as an executable. It runs merely as a series of threads. Now, those threads can communicate with one another, they would check to make sure that the BHO was there and up, and that the whatever other software we had was also up.
S: In your professional opinion, how can people avoid adware?
M: Um, run UNIX.
S: laughs]
M: We did actually get the ad client working under Wine on Linux.
S: That seems like a bit of a stretch!
M: That was a pretty limited market, I’d say.