Pew Center on Global Climate Change:

On or about November 19, 2009, as yet unknown persons hacked into an email server at the University of East Anglia’s Climatic Research Unit (CRU) in Norwich, U.K. From a much larger number of emails, the hackers selected and posted more than 1000 on a publicly accessible file server in Russia. The vast majority of the 1000+ emails are routine and unsuspicious. Perhaps one or two dozen of the email exchanges give the appearance of controversy, though no unethical behavior has yet been documented. Although a small percentage of the emails are impolite and some express animosity toward opponents, when placed into proper context they do not appear to reveal fraud or other scientific misconduct.

Here is Pew’s background document: