TOKYO (Kyodo) -- Mizuho Bank said Tuesday that its systems experienced connection disruptions from around 7 a.m., affecting online transactions for individuals and corporations, but it stressed there are no other issues detected such as a loss of customer data.

One of Japan's three megabanks suggested it may have been targeted by a distributed denial-of-service, or DDoS attack, in which networks are overwhelmed by data from multiple sources over a short period. The bank said internet transactions were functioning again by approximately 10 a.m.

The system failure led the Tokyo-based financial institution to encourage customers to use automated teller machines for urgent transactions.

Recently, a series of cyberattacks have struck Japanese companies. On Monday, Resona Bank said its internet banking service for individual clients was temporarily disrupted, apparently due to a DDoS attack.

In December, the systems of another Japanese megabank, MUFG Bank, as well as those of Japan Airlines are also thought to have come under DDoS attack.