Interesting. We could literally drown in advertising. Maybe I should completely forget the "prefab crab" project (not that I ever received a response or have found time and money to pursue it on my own).

How to tackle spam?
My first thought was via predation: what ecological niche does spam fill? Then it occurred to me that the ecology analogy might not be appropriate here because one major driving force is missing : energy costs. Spam can reproduce with virtually no energy, has no energy stored, and hence has no nutritional value!

But back in the real world (even at the nano scale) it's a different story. Those myriads of ingrained adverts take real effort to produce. If a system of genetic algorithms were in place. Inefficiencies would get rooted out , including those pesky advertising features.
Just a thought

The type of nano-factory that is developed should make a difference in the severity of the spam problem.

If the nano-factory is the type that uses solar power and simple raw materials to manufacture its products we will likely be inundated with spam. (because everything is low cost)

But if the "nano-factory" simply assembles pre-made micron scale reusable parts the problem should be more tractable. If some company makes millions of spam bots it will be significantly more expensive (the pre made reusable parts impose a greater cost) and should be easy to track back to the offending party. If one of the products of this kind of nano-factory gets infected with spam you toss it into the disassembler (all the reusable parts that contain computers must be have their programming erased during the disassembly step) and make a new object.

I'm thinking along the same lines as Jim: a more self-sustainable solution (which sounds very odd when you think about the underlying disconnect). Imagine a spammer that sets up a hydro-electric powered system. Now imagine that it's a recycling center so that raw materials are delivered by the very people it intends to spam. The output: beachballs of course! Millions and millions of beachballs (and it might look a little like this).

Well let's not pessimistically dismiss clever countermeasures against spam.

My e-mail address has been stable for more than 7 years and I only get 10 to 30 spam a day in it. I suppose if I made the first part of my e-mail address a random string, I'd even reduce even these purely dictionary attack spams on my domain name. But the amount of spams are well within the abilities of bayesian filtering to shut out.

The point is that if you are careful with your fabricator (or your e-mail address), you can reduce the amount of spam you get.

Spam is like viruses or any other biological parasite. Immune systems can never be perfect but they work well enough that species manage to thrive.

Then again, parasites do occasionally kill their hosts, especially if the death of the host ensures the reproduction of the parasite.

Sigh. Maybe I should get depressed about this.

To think our civilization could die drowning in nanotech/fabber equivalents of sketchy investment scams.

Or, getting really horrific here, to think that our planet is due to be attacked by alien spambots from a long dead civilization billions of lightyears away.