KT has discovered two additional illegal ultrasmall base stations, or femtocells, that were used to facilitate a large-scale micropayment scam, bringing the confirmed total to four.

The telecom giant said Thursday that the devices had leaked IMSI, IMEI and phone numbers, and that number of confirmed impacted subscribers had risen from 278 to 362 and that funds embezzled through fraudulent charges to gift cards and transit passes had reached 240 million won, or 173-thousand U.S. dollars. 

KT said no additional funds have been stolen since it blocked abnormal transactions on September 5, and that all newly confirmed cases predate that date.

The company stressed that personal details such as names and birth dates were not leaked via its network and that SIM authentication keys remain secure, meaning perpetrators of the data breach do not have the ability to clone impacted users' devices.

KT said it is reimbursing victims, offering free SIM card replacements and instructing customers via its website and app, as well as text message, to keep an eye out for fraudulent charges and sign up for the carrier's SIM protection service.