Is there a way to force banned users to log out automatically?

[محروم.كوم]

On one of my VB3.8 sites there are spambots registering every now and then. Fortunately the situation is well under control since they normally cannot activate their accounts through those fake emails, I also ban the IPs when I see them immediately. The problem is, well, they still visit the forum sometimes as banned users. They cannot do anything, but they are displeasing to the eye. I hate to see that from my forum's 'users online during the past 24 hours' about 3-5 of them are banned users. Is there a way to force them to log out whenever they visit the forum? Please help. __DEFINE_LIKE_SHARE__