Over the last six months, Target, Neiman Marcus, and at least three other US retailers were the focus of attacks that resulted in millions of credit card details being stolen. Earlier this month the US government sent a 16-page document to retail companies, explaining how the hacks were orchestrated. Now the FBI has stepped in to warn similar corporations that they should be prepared to deal with similar attacks. In a report sent to retail companies last week, the FBI said it had discovered around 20 cases of cyber crime against retailers in the last year.