I have learned the most important lesson about SEO the hard way: if you site gets hacked through malicious comment script, google will first black list you, and then trop your page rank. I don't know if this was done as an intended attack to my site, or by some robot, but I can see the 80% drop in traffic, even after the site was cleared with google as a clean site, and since google does not care, I think this might be a nice way to destroy your competitor's search rankings. So now it looks security matters after all.