This issue appears to have been solved (permanently?) by blocking a large number of otherwise-unused IP addresses.
This issue is currently being was at one time discussed at the ANI.
One day, I intervened in some vandalism going on at the article Vrlika. An anonymous IP was deleting relevant Serb-related content and sometimes adding unsourced, nonNPOV stuff about "Serbs aggression." The vandal began to hit several related articles, and I started reverting the vandalism all over the place - it's not like doing so is difficult or too time-consuming. The pages have been on and off page protection, and even my own user and user talk pages (and subpages) have been vandalized, as well as a short spat of vandalism of all pages that my talk page linked to. In order to make sense of this, I'm going to compile some info here about the vandal. Other users are welcome to contribute to this, because I hope it helps us keep this vandal from carrying out his vandalism. This is intended to be a helpful tool in stemming this ongoing (seemingly unending) problem.