The extent to which British betting websites are being attacked by criminals using the net to bring down a site unless a ransom is paid has been revealed by a BBC News Online investigation.
By Mark Ward
BBC News Online technology correspondent
Working with server monitoring firm Netcraft, BBC News Online has been keeping an eye on the UK's top 20 betting sites since 1 March.
Attacks took place before the Cheltenham Festival
Netcraft monitors website performance by timing how long it takes a specific server or website to respond when sent a packet of data.
It monitors the response times via servers sited in different hosting centres around the world. Servers being monitored are sent query packets every 15 minutes.
Since the monitoring started, 33 outages have been reported. Only five bookmakers have had no outages over the monitoring period.
Some outages do not last long and occur late at night and are probably connected with site maintenance rather than an attack.
Others, perhaps half of those logged, occur during the day and many show a characteristic pattern of a web server struggling to cope with the amount of requests it is getting.
BETTING SITES MONITORED
Sometimes this will be due to heavy traffic when big sports events are on such as the Six Nations and Uefa cup matches.
Occasionally the outages are caused by a Denial of Service attack.
In a DoS attack, a server is deluged with requests for information from thousands of PCs at the same time.
When this happens the response time of the server climbs before it stops reacting once it has been overwhelmed. Soon after, it recovers and the cycle starts again.
Netcraft monitors the website of the Recording Industry Association of America which is suffering a DoS attack by machines infected with the MyDoom.F worm.
Betting sites contacted by BBC News Online when these outages were taking place declined to comment on what was causing the problems.
Some sites were out of action for hours
Mike Prettejohn, president of Netcraft, said: "In the general case, we can't say authoritatively why a site isn't available, just when it isn't available."
He said surges in response times followed by an outage could be the result of a routing problem, bandwidth congestion, or server overload.
However, this week the response times from the betting sites became much easier to interpret when several sites admitted that they had been targeted by the extortionists.
William Hill, Betdaq, Totalbet and UKBetting all said that they had been attacked or received extortion demands by criminals prior to the start of the Cheltenham Festival on 15 March.
Gambling sites have been targeted because so many of the events they offer odds on are time-limited.
A spokesman for William Hill said the attack started on 11 March and continued into Friday.
"We knew we would be a target at some stage," he said.
"The crux is that we will not give into extortion," he said, "we never have and never will."
The spokesman added that DoS attacks on betting sites by extortionists were a global problem.
Irish bookmaker Paddy Power was also attacked during the Superbowl.
The sites attacked before the Cheltenham festival show the characteristic pattern of increasing response times and then suddenly no response from the server as it gets overwhelmed.
The attacks seem to be well co-ordinated as the servers being targeted are overwhelmed very quickly.
Classic DoS traffic pattern at the RIAA site
Once attacked the websites of the gambling sites stay offline for hours.
Earlier this week the website of Totalbet was offline from mid-morning on 16 March to early afternoon on the 17th in an outage that had all the signs of a DoS attack.
A spokesman for the Bookmakers Fraud Forum declined the chance to comment as he did not want to give away any information about police investigations into attacks.
A spokeswoman for the National Hi-Tech Crime Unit said: "The NHTCU is well aware of these attacks and has been investigating UK cases since the autumn.
She added: "We are working closely with the UK bookmakers in tracing and tracking down the perpetrators."
She said she could not add any more details because the investigations were active and ongoing.
Rob Pollard, from security firm Arbor Networks, said in many cases bookmakers would struggle to cope with a DoS attack because the connection to their net service provider will be swamped by bad traffic.
"It became clear quite a few years ago that DoS attacks are a service providers problem," he said.
But, he said, tools existed to help net providers spot DoS traffic and stop it causing problems for net users.