Link exchanges were once an effective way to improve search engine rankings by gaining backlinks, but are now considered spam by search engines. Search engines no longer value reciprocal links and instead focus on relevant one-way links from other sites to determine a site's importance. Participating in link exchanges can now negatively impact a site's rankings and companies have even been denied inclusion in search engine directories for using them. The best strategies now are to get relevant backlinks through directory submissions, article publishing, and social bookmarking.