The good distributors would say, ‘This is ad-supported software.” Not-so-good distributors actually did distribute through Windows exploits. Also, some adware distributors would sell access. In their licensing terms, the EULA people agree to, they would say “in addition, we get to install any other software we feel like putting on.” Of course, nobody reads EULAs, so a lot of people agreed to that. If they had, say, 4 million machines, which was a pretty good sized adware network, they would just go up to every other adware distributor and say “Hey! I’ve got 4 million machines. Do you want to pay 20 cents a machine? I’ll put you on all of them.” At the time there was basically no law around this. EULAs were recognized as contracts and all, so that’s pretty much how distribution happened.
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.
There was one further step that we were going to take but didn’t end up doing, and that is we were going to get rid of threads entirely, and just use interrupt handlers. It turns out that in Windows, you can get access to the interrupt handler pretty easily. In fact, you can register with the OS a chunk of code to handle a given interrupt. Then all you have to do is arrange for an interrupt to happen, and every time that interrupt happens, you wake up, do your stuff and go away. We never got to actually do that, but it was something we were thinking we’d do.He also talks about making his registry entries unremovable by using obscure Unicode APIs to add them and putting in characters illegal to the ASCII-based APIs most of Windows uses (oops!), writing device drivers to further pwn the hapless users' machines, and also deploying more Scheme runtime than probably anyone else:
There was also of course Scheme. Eventually, we got sick of writing a new C program every time we wanted to go kick somebody off of a machine. Everybody said, “What we need is something configurable.” I said, “Let’s install a Turing-complete language,” and for that I used tinyScheme, which is a BSD licensed, very small, very fast implementation of Scheme that can be compiled down into about a 20K executable if you know what you’re doing.
Eventually, instead of writing individual executables every time a worm came out, I would just write some Scheme code, put that up on the server, and then immediately all sorts of things would go dark. It amounted to a distributed code war on a 4-10 million-node network.So not only is a botnet of pwned Windows PCs likely to be the world's most powerful supercomputer (in purely numerical terms, at least), but a network of dodgy adware could well have been the peak of Scheme's deployment in the real world.
The author's advice to anyone wanting to avoid adware is "um, run UNIX".