The attack saw contact information for around 800 people stolen from the network.
A second person was arrested in Leeds for their suspected involvement with the Lizard Squad hacking group. In January, an 18-year-old man was arrested in London on suspicion of carrying out cyber-attacks that crippled the PlayStation and Xbox Live networks in late 2014, for which responsibility was claimed by Lizard Squad.
A 21-year-old man was arrested in London on suspicion of being part of the D33Ds Company hacking collective, who are believed to have been behind a 2012 cyberattack on Yahoo, which saw the theft of more than 400,000 email addresses and passwords which were later published online.
The NCA's "strike week" saw 25 operations carried out across the UK and those arrested are suspected of being involved in a range of cybercrimes, including data theft, fraud and creating computer viruses.
Specialist officers from regional organised crime squads worked with the Metropolitan Police, the NCA and the National Cyber Crime Unit (NCCU) to make the 56 arrests. The biggest operation took place in London and Essex and saw 25 people arrested on suspicion of using the internet to steal money, launder cash and carry out other frauds.
