Google will not be displaying hacked websites in the search results for roughly 5% of search queries. This means sites that are vulnerable to hacked spam such as malware download, promotion of traffic to low quality sites, porn, and marketing of counterfeit goods or illegal pharmaceutical drugs, etc. will lose their percentage of share.
What Should the Webmasters Do?
The webmasters should not leave their site vulnerable to hacking. If the hackers feel free to pass through the site then Google might drop the website from getting displayed in the search results and all the hard work done to get good rankings on Google should get wasted.
For more help for hacked sites, please have a look at the below video:
Further Reading: Webmasters help for hacked sites
Source: Update on how Google tackles web spam
3 Methods for Easier Management of Site Verifications
Search Queries in Webmasters Tools
How to Find Out the Total Number of Pages Blocked by Robots.txt