Google Panda Update Overview: Panda Recovery 18 July 2013
This update is designed to reduce rankings for low-quality sites—sites which are low-value add for users, copy content from other websites or sites that are just not very useful. At the same time, it will provide better rankings for high-quality sites—sites with original content and information such as research, in-depth reports, thoughtful analysis and so on.
Penguin 2.1 (5) - October 4, 2013
Many in the SEO community have speculated that some contributing factors to Penguin might be things like:
1. Aggressive exact-match anchor text
2. Overuse of exact-match domains
3. Low-quality article marketing & blog spam
4. Keyword stuffing in internal/outbound links