i am a newbie when it comes to html, but i found a website called
http://stretchmark-creams.org/

and it has 2 million backlinks, but every backlink is inserted into the soruce code on other websites! how does he do that?

i could not finde a plugin with hidden backlink that the "infected" website had, everything seems legit.

one backlink i found

it is on this webpage http://castrof.eu/ but you cant finde it, but if you view source code you will finde it. search for best stretch mark cream and you will finde

'"' + '>');</script><div>

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<a href="http://besteye-cream.org">Best Eye Cream</a> <br/>
<a href="http://stretchmark-creams.org/">Best Stretch Mark Cream</a> <br/>
<a href="http://darkcirclesunder-eyes.com">Dark Circles Under Eyes</a> <br/>
<a href="http://howtogetridof-dandruff.com/">how to get rid of dandruff</a> <br/>
<a href="http://skin-idreviews.com/">Skin Id Reviews</a> <br/>
<a href="http://murad-reviews.net/">Does Murad Work</a><br/>
<a href="http://doesproactiveworks.org/">Does Proactive Work</a>
</div>
<script>document.write ('<' + '/d' + 'i' + 'v>');</script>

how does he do it?