In an statement posted on its site, Betfair told its users that it been the victim of a distributed denial of service (DDOS) attack. DDOS attacks are used by malicious Web users to prevent a server from functioning properly by flooding it with traffic.
"Betfair [has] experienced a distributed denial of service (DDOS) attack by criminals using the Internet which affected the main exchange website between 16:40 and 17:45. We would like to apologise for the inconvenience caused by this action which was entirely outside of our control," said the company's statement.
The attack prevented some users from accessing Betfair. Its betting exchange lets punters place bets or offer odds to other users, allowing them to back an outcome or wager that it will not happen (a practice called 'laying').
Several customers complained on Betfair's forums that they were unable to view or place bets, and some claimed that they had lost money.
Many Internet gambling firms have been targeted by criminals threatening to attack their sites unless they pay protection money. Back in February, Betfair said that this was a serious issue, but didn't say whether it had received any specific threats.