The mobile phone company Three has experienced a fresh data breach Attack.Databreach after some customers logging into their accounts were presented with the names , addresses , phone numbers and call histories of strangers . Three said Vulnerability-related.DiscoverVulnerability it was investigating Vulnerability-related.DiscoverVulnerability a technical issue with its systems and urged those affected to contact its customer service department . One customer , Andy Fidler , told the Guardian he was presented with the data usage and full call and text history of another named customer when he logged in on Sunday night . Another , Mark Thompson , said on Facebook he received a call from a complete stranger who said she had logged on to her account and was shown his details . Thompson said it was a “ shocking breach of data privacy Attack.Databreach ” . He wrote on Three UK ’ s Facebook page : “ Care to explain just how my details have been shared , how many people have had access Attack.Databreach to my personal information , for how long , and how many of your other customers have had their details leaked Attack.Databreach by yourselves to other members of the public as well ? ” Other customers also wanted to know why they were being presented with other people ’ s information when they logged in . Three UK , which is owned by the telecoms giant Hutchinson and has 9 million customers in Britain , said it was investigating . “ We are aware of a small number of customers who may have been able to view the mobile account details of other Three users using My3 , ” a spokesman said . “ No financial details were viewable during this time and we are investigating the matter ” . The Information Commissioner ’ s Office said it “ will be looking into this potential incident involving Three ” . A spokeswoman for the regulator said : “ Data protection law requires organisations to keep any personal information they hold secure . It ’ s our job to act on behalf of consumers to see whether that ’ s happened and take appropriate action if it has not ” . The problem comes four months after three men were arrested after fraudsters accessed Attack.Databreach personal data of thousands of Three customers , including names and addresses , by using authorised logins to its database of customers eligible for an upgraded handset . Customer information from more than 133,000 users was compromised Attack.Databreach in the incident Attack.Databreach .