A man in Nevada has pleaded guilty to sending more than 27 million spam messages to Facebook users.  The outcome of this case could impact user experience for Facebook fans across the world.   NBC reports that U.S. Attorney Melinda Haag said on Monday that Sanford Wallace of Las Vegas admitted to accessing about 500,000 Facebook accounts and sending "unsolicited ads disguised as friend requests" over a three-month period. The scam artist collected Facebook users' account information by way of sending "phishing" messages, tricking users into providing their passwords. He then used the information to log into users' accounts and post spam links on their friends' walls. The Internet traffic provided by those links generated payments for Wallace. Appearing in federal court, Wallace admitted to accessing Facebook's computer network to send the spam messages on three separate occasions.   The 47-year-old also violated a court order not to access Facebook's computer network, and has been charged with fraud and criminal contempt. Mr. Wallace was freed on bond and will be sentenced in December. He is facing a potential fine of up to $250,000 and three years in prison.