It's a spam bot, I have got rid of it. As why it's always viewing "forum list", very simple, it's programmed to do so. The "forum list" is our homepage, maybe the spammer behind the bot only needed the information on our homepage, or maybe it's programmed to access every new thread but go back to homepage after the visit, which makes it less noticeable.
Obviously this is a stupid bot, it should logout every time after it finishes its job, it's just a matter of seconds, it would be hard for us to notice it.
I hate to see such bots on our online member list, so I screen the list a lot and check out unfamiliar names, usually I get rid of them in the first hour or day. Had no idea how I overlooked this one and allowed it to exist for so long.

It's not unusual to have a dozen bots like this one registered within one day.
What's even weirder? Some banned bots will access the forum regularly for years, I had to actually delete the accounts to avoid seeing them. You see, the spammer behind the bots don't even know the status of their bots, it's possible to have hundreds of spam bots visiting hundreds of forums 24/7, as long as their computers can handle it.