What you are dealing with is a ton of bots, spiders, search engines crawling your forums all at the same time.
What do you have your session timeout set at? If you have it really high it would be a good indication of why you have so many guests in your whos online. using Simon Lloyd's Ban Spiders by User Agent will help you a lot to help combat this.
You will also have to use some IP blocks in your htaccess to stop Chinese bots from hitting your site, which is what Baidu is , they just don't care about rules and will just hit your site or forums like they are going out of style.
You should have this taken cared of in a couple of hours, if you need help let me know, take a look at this thread to help you more if you feel you can do what we did for Dave's website.
https://vborg.vbsupport.ru/showthrea...53#post2448953