I suggest using a dictionary to come up with "names" of anonymous users:

aback abacus abalone abandon abase abash abate abater abbas ...

You could pick them in random order, or sequentially.

... John Gilmore

certainly dictionary words are good, randomly, not in sequential order. But also usernames such as cs135 and anything else. The point is not to form any pattern distinguishable from the actual distribution of usernames in the real world. So some would even look like univ. course accounts, even with a couple "anon"-looking usernames thrown in! an analysis of actual usernames should be in order for this, and the actual types and probabilities.... in other words, take this situation full throttle! and of course, we need not give up our legal rights to use email. but we must, IN ADVANCE, be prepared and be already fully set for anything! dan