Blackhat SEO, or spam-seo, is a malicious technique used to manipulate the search engine results in order to benefit a website in terms of relevance.
The payload is HTML based, thus intended for client-side use and the payload is executed after the infected page is loaded directly in the browser.
Malware creators are trying to avoid the visual detection of the injected spam by hiding it out of the visible browser area. One of the ways how to achieve this is using of the "negative positioning" technique.
Affecting
Any type of site.
Cleanup
Investigate your site's files in order to find any hidden div that wasn't added by you. Remove all malicious code found.
Dump
<div style="position: absolute; top: -999px;left: -999px;">
<a href="http://www.--domain_removed--.com/">Karen Millen Sale</a>
<a href="http://www.--domain_removed--.com/">Karen Millen Australia</a>
<a href="http://www.--domain_removed--.com/">Karen Millen Dresses Australia</a>
<a href="http://www.--domain_removed--.com/">Karen Millen Ireland</a>
<a href="http://www.--domain_removed--.com/">Nike Free Run UK</a>
<a href="http://www.--domain_removed--.com/">Karen Millen UK</a>
<a href="http://www.--domain_removed--.com/">Salomon Shoes UK</a>
</div>