A woman uses her mobile phone as she walks past in front of an Optus shop in Sydney, Australia, February 8, 2018. 2 telco Optus, owned by Singapore Telecommunications Ltd (STEL.SI), said it will contact up to 10 million customers whose personal details were taken in a "sophisticated" hack, but added no corporate clients were compromised. As many as 9.8 million accounts may be compromised, equivalent to 40% of Australia's population, but "that is the absolute worst case scenario (and) we have reason to believe that the number is actually smaller than that", Bayer Rosmarin said. Police and cybersecurity authorities were still investigating the attack which Optus told customers about on Thursday. As a major telco, Optus considered itself a target for cyber attackers and routinely repelled attempts to breach its systems but "this particular one is not similar to anything we've seen before, and unfortunately it was successful", she said.

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