Google announced launch of new hacked site algorithm with the aim to help users and webmaster from hacked spam both in websites and Google search results. It is observed that in last few month there is increase in website hacking by spammers affecting most of legitimate sites and used to engage in traffic to low quality and illegal products websites or malware download etc.
The legitimate sites affected are Government, Education, Hotels, Shopping and Blogs etc. This happened because webmaster or site owners do not follow standard best practices for security and leave their websites vulnerable to being easily hacked. WordPress and Cpanel are the main area where hacker attacked.
Matt Cutts also tweeted that
Google is launching some improvements for hacked sites
Google has spotted such websites and cannot penalize as webmaster or site owner are ignorant about this hacking. Hackers and cybercriminals compromised the sites and inject low quality pages or redirect to again traffic to low quality pages or websites.
The new hacked sites algorithm will affect 5% search queries which is pretty high and will be rolled out continuously. You will see that in case of certain queries on search results you may not see the all results but few. For example Google shows 10 results per page but in case the search queries is consist of hacked pages you may see less than 10 i.e 5 or 6 pr 7.