Hackers broke into 24,000 Club Nintendo accounts after pummelling the loyalty-reward website in a month-long assault.
The games console titan revealed that the sustained brute-force attack exposed the names, addresses, phone numbers and other personal details of thousands of its customers.
Nintendo has reset a number of passwords as a first step towards resolving the problem. Hackers began probing Ninty's network on 9 June, but their volleys were only detected nearly a month later - on 2 July.
An investigation subsequently uncovered evidence of more than 23,926 unauthorised but successful logins. Nearly 15.5 million logins were attempted during the cyber-battering, The Japan Times reports.
Club Nintendo allows players to gain points by purchasing games or consoles. These points can be redeemed for goods such as CDs, and it is likely that this is what motivated the attack. The console maker is promising to beef up security in the wake of the assault, one among a growing list of security incidents involving video gaming firms.
A Nintendo representative told gaming news site Computer and Video Games that only users in the Wii maker's home turf of Japan were affected.
Last week games publisher Ubisoft announced that in had fallen victim to a hack attack, prompting a decision to force a reset of customers' uPlay passwords. Neither the Ubisoft nor the Nintendo breaches involved financial records.
Both were on a much smaller scale than the infamous PlayStation Network breach of April 2011, which led to the suspected compromise of 77 million accounts. PSN was taken offline for more than a month to sort out the resulting mess, the worst of its kind in history. ®