This post will be a bit in length.
Our anti-proxy measures are at very full throttle, such that if we turned them up any more there would be risk of blocking legitimate users by mistake. One or two might be blocked once in a while already. These measures block known proxies and bots and "naughty" IP ranges by querying several public real-time intelligence databases that keep track of these things through a number of techniques.
In addition, our new post / new thread forms have several invisible countermeasures designed to trick common and less common bots into revealing themselves and block them from posting. These include extra fields that normal web browsers know to ignore while rendering the page, which look to a bot like they should be filled out and if tripped will block the post, as well as hidden fields with randomized access keys pre-generated into them that will trip the system if they are altered or omitted. Most generalized bots, even many finer-tuned ones, fall prey to these automated defenses, and there are several more active and automated defenses embedded in the Vichan software.
Furthermore the mods rove when they have time and ban bots which I believe have been designed with the specific capabilities to outsmart Vichan's particular automated security measures. These we can do nothing about except to deeply alter the code or to enable captchas, which most people don't have time for or don't want respectively.
The last measure would be to hire Janitors. Unfortunately I have been busy lately, but I am planning and considering a new application process to be started soon if this wave of spam doesn't end, which I don't really expect it to, but I can hope. I'll get around to it when I can. Until then, I trust my staff to keep a watchful eye for the bots that have been bothering us lately.
TL;DR We have been and will continue to be working on it, far beyond what most of the users and the bots are aware of.