Matt Cutts has recently revealed in a video entry that 90% of all messages sent out via Google Webmaster Tools are issues related to Black Hat SEO.
For all you guys that are new to SEO. Earlier this year, during the months of January and February, Google had introduced their new unnatural link warning messages. These messages were directed at websites which contained suspicious behaviour of unnatural incoming links (paid links or low quality links). Websites which received these notices were either warned or had immediately incurred ranking penalties.
A total of 700,000 messages were sent out, meaning that just over 600,000 of those messages issued were in regards to Black Hat. Quiet a figure really..
Check out the video below and feel free to comment.