Thanks @Chbaca - I reckon it's some kind of spam bot (?) because it is precisely written in this way ".../Detected" and is across multiple sites that have no relation to one another and are in some cases on different servers altogether. I have a sneaking suspicion there is some kind of spammy bot that tries to look for the presence of a malicious page and somehow this is being submitted to index.
Anyway, thanks for noting it, we'll just do 301 if it keeps cropping up.