This update has received very vague credentials by Google. ("No, this is not the Penguin update" was the most official reference given to the update - https://twitter.com/mattcutts/status/332914600095907840)
Many site owners have reported significant falls in ranking.
An analysis of the update found the following to be affected:
1. Sites that have cross-links (web site structure).
2. Sites with many outbound links that are a Follow links.
3. Sites with a problematic link profile: spam comments, many links from indexes, etc.
4. Sites that did scarping to other sites (for example sites that have created news summaries with links to full articles on other sites)