Last week, Google announced a new feature which displays an alert within search results that tells a user that website may have been hacked. Google has been taking website safety seriously since 2008 when malware warnings were displayed when you click through to a site. An example of the latest warning is featured below. The warning simple says "This site may be compromised" and links to this help page. Google's help pages note that a compromised site has not necessarily detected malware - if that was the case, the warning would say "This site may be harmful to your computer."
Part of the reason for the update is that not all webmasters regularly login to their webmaster tools account and consequently miss some of the warnings regarding their site. By displaying in search results, users will be able to alert webmasters and also webmasters are more likely to discover it from routine checks of their performance on the search engines.
As the alert displays within search results, webmasters may see a loss of traffic if the warning is displayed, adding further incentive to maintain website security. If your website unfortunately returns such an alert then you may request a review to speed up removal of the alert once the problem has been rectified.