Three UK has announced a significant data breach as personal information of up to six million customers is put at risk.

The team has admitted hackers successfully accessed customer upgrade databases using employee log in details, according to the Telegraph. Although numbers are unconfirmed it is believed two thirds of the nine million UK customers are now exposed after the incident. Exposed data includes names, phone numbers, addresses and dates of birth, but not financial information, the team claims.

“We’d like to reassure customers that their financial details are not at risk,” the company said on its website. “We are investigating how many customers are affected and will be contacting them as soon as possible. We’ll update with further information once we have this.

“Over the last four weeks Three has seen an increasing level of attempted handset fraud. This has been visible through higher levels of burglaries of retail stores and attempts to unlawfully intercept upgrade devices.

“We’ve been working closely with the Police and relevant authorities. To date, we have confirmed approximately 400 high value handsets have been stolen through burglaries and eight devices have been illegally obtained through the upgrade activity.”

Although early days, Three execs have more than enough to be concerned about following the fallout of TalkTalk’s breach earlier this year. During this incident, details of 150,000 customers were stolen. As a result of this incident 90,000 sought services elsewhere with some estimates stating it cost TalkTalk as much as £60million.

Three has been making solid progress in the UK market since its entry in 2003, and is now recognized as one of the major players in the market. On its website it claims to carry 37% of the UK’s mobile data traffic, have 9.2 million customers, 4.9 of which are 4G, using 5.4GB on average every month. So far in 2016 the teams operating profit is £348m.

TalkTalk suffered at hands of the industry mainly due to the fact financial information was stolen. The Three exec team claim no financial data has been stolen, however the numbers are slightly different. 150,000 TalkTalk customers were exposed, compared to potentially 6,000,000 Three customers. Whether the claim financial data is secure will prevent a customer exodus remains to be seen, but it’s far from ideal for the Three team.