Google just launched a site called Webmasters help for hacked sites that walks you through the steps required to get your website back on Google\’s good side if you see something like this in search results for your website:
Typically the only time I\’ve seen sites get hacked is when people have used WordPress themes or plugins that come preloaded with malware or other junk and don\’t even realize it. That\’s why I always recommend downloading your themes and plugins from reputable sources like the main WordPress download site, or other theme builders with a good reputation (i.e. WooThemes, Studiopress, The Theme Foundry or ThemeForest).