The government has confirmed that the recent malware attack on SK Telecom(SKT) resulted in four kinds of information leaks that could be used to duplicate customers’ SIM cards.

In announcing the preliminary investigation results on Tuesday, the Ministry of Science and ICT said a public-private joint team found that subscriber phone numbers and international mobile subscriber identity numbers were exposed, along with 21 types of information that SKT uses to process cellular data.

But the ministry said the leaked information did not include international mobile equipment identity numbers.

As a result, the ministry said subscribers who sign up for SKT’s SIM protection service can prevent fraudsters from accessing their accounts even if their SIM cards were duplicated and inserted into other mobile phones.

The team looked at five SKT servers that came under attack and is expanding the investigation to determine whether other servers were affected.