But for you to know they were on almost the entire day, you'd have to have been on longer.
Does that mean that our beloved brother Trevor is really a bot?

To be slightly more serious, I don't think it would be possible to detect and delete all the bot accounts. On a previous website I used to moderate, removing spambot adverts was pretty much a full-time job. It is easier nowadays to stop them setting up in the first place, but it would still take time to get rid of the ones who get through.