Looking into the issue you described...
OK, based on my initial research into this issue, and I could be wrong... I am leaning towards calling this a quirk in how the new "spam diff" works, which is a new feature in 1.17 or 1.18 of mediawiki. When it is showing you all those lines that it wants to remove, it is on the spam protection page, right? So it is not actually erasing stuff. It just looks like it wants to erase stuff. But this may be a quirk in my spam code with the new mediawiki feature.
So quick summary - I think the wiki is safe, unless you actually *see* the wiki erase lots of content like the spam protection page is making you think it wants to do. I think I just need to fix the output of the spam protection page.
If you actually see data being destroyed, let me know. But even then, the wiki has history. So don't be afraid of editing and don't be scared by the spam protection warning at this time.
UPDATE: I have added some URLs to the whitelist so the installation tutorial isn't set up to trigger the spam filter out of the gates. You should now be able to save changes to this page.
UPDATE: OK, the strange thing is that you should not have been able to make any changes to the Installation Tutorial on the wiki like you did, since this page had links in it that triggered the spam filter. Did you do anything special to get by the spam filter? I will look at the code and make sure it is applying to you.
Reply: Ah, ok, that makes perfect sense re: you editing sections and not the whole document. You may want to try switching your UI to English and seeing if that makes things work correctly when the spam protection filter does trigger. Yes, the spam protection filter seems to check against the entire contents of the new page (or if editing just a section, the section). So any existing links in the page or section will trigger the spam filter. This is explained in the Engilsh spam filter message but I don't have a German variant :)