The lottery website was down for more than two hours. Many customers who were trying to buy tickets from the operator Premier Lotteries Ireland (PLI) for the €12m (£9m) prize money were not able to buy the tickets.
A statement from PLI said: "Indications are that this morning’s technical issues were as a result of a DDoS attack affecting our communications networks.
"The issues were resolved by the National Lottery’s DDoS protection systems, limiting disruption and restoring all operations within two hours. This incident is still under investigation.
"However, we can confirm that at no point was the National Lottery gaming system or player data affected."
As reported by BBC, at around 11:21 GMT, the attack started and it continued for more than two hours.
Data and gaming systems remained unaffected but, due to heavy inflow of traffic, it denied access to those who were trying to buy lottery tickets.
The website recovered from the attack at around 13:25 GMT and the website showed a message flashing its customers that it was free from DDoS attacks and it was protected by CloudFlare.
CloudFlare programmer, John Graham-Cumming said: "the thing to note was the machines used to issue lottery tickets were also affected, meaning there was no way anyone could purchase a ticket for the draw.
"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."
Some security experts think that due to a massive surge in traffic at certain times might have caused it to become unresponsive.