The immigration department has confirmed that the emails sent to green card lottery winners requesting for money are fake. The U.S. government asks for money only once after the visa interview process begins. The immigration department has been getting mails from green card lottery entrants questioning the authenticity of such mails. One such mails asks a green card aspirant to deposit 880$ via Western Union to someone in the United Kingdom.
Turns out that the green card lottery scam has gone global. People wanting to apply for green cards are fleeced. It makes a fool out of green card aspirants, by making them believe that they have won a United States diversity Visa and they have to pay money upfront to get it.