Recently I've been having a lot of weird looking requests that would end up reported in Errbit. Initially I thought that it is my fault but after double checking all the JS code, I would still get those errors.
Fixing this is quite easy. Undefined/cache/xxx requests come from Complitly malware chrome plugin. Solution to this is quite simple (source). Just add this to every page you have (or every with a form):
this will stop the malware script.
The second issue:
ArgumentError: invalid %-encoding (arizona1�0���U��� scottsdale1%0#��U� ��starfield technologies, inc.1301��U���*http://certs.starfieldtech.com/repository/1402��U���+starfield secure certificate authority - g2/html>)
The rest of weird requests was coming from EasouSpider crawling engine. So just:
User-agent: EasouSpider Disallow: /
and don't care anymore.