The company was forced to take action after being hit by a warning attack, which blocked visitors to one of its websites last year. It was followed by a $10,000 (£5,300) ransom demand and the threat of another attack.
IT staff had to work through the night blocking attacking IP addresses when the gang struck again three weeks later. The criminals were able to counterattack by reconfiguring their bot networks - networks of hacked PCs used in denial of service attacks - to evade the blocks.
"They started with a relatively small attack and were building up over 24 hours. After 24 hours, which was a Sunday night, they had pretty much taken down the whole site," said Sporting Index IT director Hugo Smith.
The IT team looked at possible countermeasures and came up with three options: install its own blocking technology, buy a system from its ISP or use a proxy blocking service.
"The first two options would have cost a lot more. We would have had a huge capital investment, probably £200,000, and we would have had to wait eight weeks for delivery," said Smith.
Sporting Index redirected its internet traffic to Prolexic, a specialist in blocking denial of service attacks, by modifying its domain name server details.
The service uses high-speed grid computers to remove attack messages from internet traffic in real time before returning a clean stream back to Sporting Index.