Ireland’s National Lottery website and ticket machines were knocked offline after a distributed denial of service (DDoS) attack on Wednesday.
Customers trying to buy tickets for the 12m (£9m) draw found themselves unable to do so for nearly two hours.
The jackpot was the largest in 18 months.
Premier Lotteries Ireland (PLI), the operator, has said the incident is under investigation.
During a DDoS attack, a website or online service’s capacity to handle internet traffic is overloaded – usually by automated programs set to flood the site with requests.
The attack began at 11:21 GMT on Wednesday and lasted for about two hours.
Retail systems were brought back online by 12:45 GMT and the website by 13:25 GMT.
“They said you couldn’t buy tickets from the ticket machines, which is really interesting, it’s not just the website – it would be quite interesting to understand why that happened,” said John Graham-Cumming at DDoS-protection company Cloudflare.
“This incident is still under investigation,” a spokeswoman said.
“However, we can confirm that at no point was the National Lottery gaming system or player data affected.”
Given the large jackpot involved, the lottery was experiencing high demand for tickets on Wednesday lunchtime.
The impact of the attack may well have been heightened by this, according to Igal Zeifman, senior digital strategist at cybersecurity company Imperva.
“As a rule, record-setting prizes and jackpots result in traffic spikes on lottery sites, and it is very common for DDoS attackers to strike during such predictable peak traffic times, especially when going after big targets,” he said.