As a side note you should show guests as little as possible, one thing thats a load on your server is showing the "who's Online" to guests, disable it for them. Try to cut down on the amount of things you let them see, also with my mod, if they still exist in your list, prune out "custo" and "DA".
Mostly when you see a bot/spider on your forum you can enter it's name (one name on one line) in the list and after your whos online timeout period has expired the offending bot will be no more

, some bots have variations of their name in their useragent and some dont have their display name in the useragent string at all!
make sure you make use of these tools in the mod description here
https://vborg.vbsupport.ru/showthread.php?t=264932