to buttress the general roboting-out of the piwik directory. (I don't keep the tracking code on the page itself. It's huge! There's a separate copy in each site's /piwik/ directory, and the database itself lives my personal site.)
I also have a targeted rewrite of requests for piwik's tracking dot-- the one that lives inside <noscript> tags. In rare cases it happens to be the only image on a page, and then places like facebook go berserk asking for it. So instead I rewrite to a site-specific small logo-- the kind you'd use as a link.
Have you tried the piwik forums? Someone generally knows what's going on. There's also an area in your piwik prefs where you can tell it to ignore specified IPs. I don't know if you can set it for ranges; otherwise it's just "ignore me" and not useful for much else.
:: idly wondering if many people have interesting personal scripts masquerading under the name "piwik.js" since there would otherwise be no reason to even ask for the file ::