East Japan Railway Co. has suspended a credit-swapping service for its Suica electronic fare card users after detecting a wave of unauthorized log-in attempts on its website.

JR East said Tuesday it found signs of unauthorized access to its Suica Point Club website at around 9:30 a.m. Monday. A subsequent probe revealed that roughly 940,000 log-in attempts had been made since around 5 p.m. Sunday, of which about 19,000 were successful.

While saying there was no evidence that credit was stolen, JR East is warning account holders who logged into between Sunday and Monday to change their password.