Panda: Feb 23, 2011
The first major algorithm change affected roughly 12% of searches. It focused on quality and user experience. It cracked down on thin content sites, content farms, and sites with too many advertisements in proportion to amount of content, etc. This was an all-out assault on web content. It looked for the amount and quality of content that appeared ‘above the fold’. THAT SAID: your quality content should start as close to the top of the webpage as possible. And don’t clutter your site. Content must be well-written, well-researched and error-free. You must take the time to answer questions — in the best possible manner.
Penguin: April 24, 2012
This was the next in a string of algorithm adjustments, affecting about 4% of search results. It targeted those who were severely over-optimizing their content, for example using ‘Black Hat SEO’ (stealth) techniques such as keyword stuffing, hidden text, sneaky re-directs, etc – BUT it also went further than that. It also targeted Link Schemes (i.e artificial links). Google used a formulaic approach to find the artificial links, i.e. if you went from 10 to 10,000 links in one month. Penalized sites were sent to google’s Sand Box, where sites were punished by going to the bottom of the rankings.
Hummingbird: August 30, 2013
After the dust settled on the prior adjustments, google released its latest big algorithm update, which focused on contextual search and the semantics of search. It moved away from indexing for specific keywords and moved towards more LSI (Latent Symantic Indexing) — comparing words based on mathematical computations — so that google can ‘understand’ words and their relationships (i.e. Best Diet Tips = Nutrition Advice for Weight Loss). It also moved toward understanding questions and their answer (i.e. what is the weather in NY). In a nutshell, this was a complete overhaul of google search — it affected 90% of searches on google.
Mobilegeddon: announced in late April 2015
Impacted 60% of all searches but has far reaching implications. Web design needs to take mobile into account, as well as tablets, etc. This is going to be an important factor going forward. You must approach your site with a design perspective as well as a content perspective. Your site must work well on all browsers AND all devices including Phones and Tablets.