We block the memberships of around 50 spam merchants every 24 hours Lutz and although some of the 'goods' advertised may be of Chinese origin the majority of spammers advertising them are from Russia, the Ukraine, Lithuania, USA, then just a couple from China, Israel and the Netherlands according to their email domain names. Some use 'cc' which is a commercial domain often used by spammers who could be anywhere.
Many of them use automated web crawlers to find susceptible websites with no anti spam filters. Forum moderators usually manage to block the majority of illicit 'memberships' before thay have chance to do any harm or place adverts but one or two slip through and their spam is deleted as soon as we see it and their access is blocked.
The spam may not be originating from your computer Lutz but take care not to get ripped off. Until the powers that be from Haymarket get their act together we'll just continue to delete spam placed overnight and block all suspicious 'memberships'.