Google has begun rolling out a series of algorithmic changes designed to more aggressively target hacked spam. These changes will affect roughly 5% of queries when fully rolled out.
Google says its approach to hacked spam is getting more aggressive in order to protect searchers and site owners. Perfectly legitimate sites can become dangerous if they fall into the hands of hackers.
A site hack can lead to malware downloads, marketing of illegal goods, or can be used to redirect people to low quality sites the didn’t intend to visit.
For certain queries, Google says you may begin to see a reduction in the amount of results shown. This is because Google wants to show only the most relevant results for particular queries.
With Google removing large amounts of hacked spam from search results, SERPs may begin to get smaller. An example is given in the announcement showing about a quarter of of a search results page being removed.
This is said to be an ongoing effort from Google to continuously fine tune its algorithms to weed out bad content.