“Anonymous”, a group of hackers who originated on the imageboard 4chan, has been targeting different organizations since their beginnings in 2003. They recently released this video, announcing plans to target Walmart.
Among Anonymous’s previous targets are businesses like Sony and Aiplex (an Indian company that was contracted by ilm studios to target sites with pirated material, like the Pirate Bay), Law Offices in Britain, services like Amazon and Paypal, and even the Church of Scientology.
Typically, the hackers will obtain access to their targets’ websites and then proceed to wreak havoc. This includes fake-posting on the site, disrupting its operations and, if possible, shutting it down completely.