Anonymous is a collective of unknown, unnamed people associated through the internet, and in this case the term refers to an organization of hackers who claim they safeguard the public good. Zynga is a video gaming company famous for its Facebook-based game Farmville.
Anonymous released a statement on AnonNews.org detailing a wonderfully dramatic kind of blackmail that could save almost 800 jobs. I'm not a fan of small groups claiming to represent the greater majority, but this suggestive of an epic battle along the lines of Clark Kent versus Lex Luthor. Anonymous has apparently hacked into Zynga's servers and extracted games that normally cost money, threatening to release them to the public for free unless the company "will cease immediately the plan."