The latest disclosure of NSA whistleblower Edward Snowden's top secret documents via The Intercept revealed US and UK intelligence agencies had been hacking into leading SIM card producer Gemalto's network and stealing its encryption keys.
Subsequently, the security breach enabled the UK Government Communications Headquarters (GCHQ) and the US National Security Agency (NSA) to monitor mobile phone calls and data transfers across the world from 2010.
"Gemalto is the world's largest manufacturer of SIM cards, so they are also available in Swedish mobile phones," Henrik Westman, head of media relations at TeliaSonera, was quoted as saying in the publication.
However, according to the company's Finnish branch, as many as half of the country's three million TeliaSonera subscribers use SIM cards manufactured by Amsterdam-based Gemalto.
Elsewhere, Germany's Deutsche Telekom expressed concern that its customer base may have fallen victim to the attack, while Russia's two largest mobile phone operators ruled out substantial security concerns involving their users.
Other major operators using Gemalto's SIM cards include AT&T, T-Mobile, Verizon and Sprint.
The latest revelations are part of 1.7 million classified documents leaked by Snowden, a former NSA contractor, in July 2013, setting off a US mass surveillance scandal.
