Deliberately broken links
Stops the linked site from knowing they've been linked to by 4chan. Many websites check the referring page ("HTTP_REFERER") and may block it; this workaround forces the viewer to copy and paste it. The most common method of breaking links is to remove the leading 'h' from the URL and replacing it with 'x' (xttp://google.com, for example). Amusingly, this is a futile gesture on 4chan, as the software doesn't create hyperlinks for any URL; any message that does have live links in it was either posted or edited by a mod.