>> That is the real Erwin Moller.

Ok, thanks for the clarification. The email address just looked
suspicious. =)

>> Correct me if I'm wrong, but if user left his site, and then returned
refer would point to the other site. So detecting refer value could
possibly help the problem.

Great, I'll try that out then.

>> Refer it's send by the user, so can't be trusted. You can use it
to improve the functionality of the site, but don't use it to any
critical checks (like access controll ect.).

It's just to display a welcome message, so no problem there.

>> It's also possible, that refer will be empty, when user types in the url
or opens new window in 'new tab' (not sure about that though).

Right. Well, thanks for all of the suggestions.

Regards,
- Sebastian