The top two most commonly requested nonexistent pages on my WordPress website are the following:
I use the Redirection plugin to track 404 requests, and these are the most common ones, with the next most common being requested only 50 times.
Why would these pages be requested? I speculate that these are HTTP error codes based only on the URLs, but I have never seen either a 403 or 408 HTTP error returned by my website. If those HTTP errors were being returned, would these pages be requested, or would the site just return a blank page and the error code?
Interestingly, the vast majority of the
/408.shtml requests are from the same user agent, "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:40.0) Gecko/20100101 Firefox/40.1" with no referrer, whereas the
/403.shtml requests have a wide variety of user agents, but all include
/403.shtml itself as the referrer. Based on IP geolocation, the vast majority, if not all of these requests are from bots not humans.