The UK’s Information Commissioner’s Office has slapped TalkTalk with a £100,000 fine for breaching the Data Protection Act.
The fine relates to 2014, when the personal data of up to 21,000 customers was accessed unlawfully by three accounts belonging to IT services company Wipro.
At the time, TalkTalk outsourced some customer service work to the India-based company.
An investigation was launched after an unspecified number of TalkTalk subscribers complained in September 2014 that they were receiving scam calls in which their addresses and account numbers were quoted.
This revealed that 40 Wipro employees had access to data belonging to 50,000 TalkTalk customers.
The staff could access the data from any internet-enabled device, the ICO said, with no controls in place to restrict access to devices linked to Wipro.
Although the UK government body did not find direct evidence of a link between the compromised information and the complaints about scam calls, it said a lack of adequate security measures had left customer data open to exploitation by “rogue” employees.
Moreover, it said TalkTalk had failed to implement measures to stop the problem despite having had “ample opportunity over a long period of time” to do so.
It is the second time in less than a year that the ICO has fined TalkTalk.
Information Commissioner Elizabeth Denham said: “TalkTalk may consider themselves to be the victims here.
“But the real victims are the 21,000 people whose information was open to abuse by the malicious actions of a small number of people.
“TalkTalk should have known better and they should have put their customers first.”
In a statement, TalkTalk said: “We notified the ICO in 2014 of our suspicions that a small number of employees at one of our third party suppliers were abusing their access to non-financial customer data.
"We informed our customers at the time and launched a thorough investigation, which has led to us withdrawing all customer service operations from India.
"We continue to take our customers’ data and privacy incredibly seriously, and while there is no evidence that any of the data was passed on to third parties, we apologise to those affected by this incident.”