HMRC 'security incidents' double in Wales over five years
The number of "security incidents" across the five tax offices in Wales has almost doubled in five years.
The figures have risen from 807 in 2014-15 to 1584 in 2018-19, BBC Wales has discovered.
Unauthorised disclosures - data revealed to the wrong people - has also doubled.
An HM Revenue and Customs (HMRC) spokeswoman said "we take all security incidents seriously and ensure that lessons are learnt from all cases".
The bulk of the incidents, at offices in Swansea, Wrexham, Porthmadog and two offices in Cardiff, were "unauthorised disclosures" of data.
This category of incidents increased from 642 in 2014-15 to 1353 in 2018-19, according to information obtained using a Freedom of Information request.
HMRC point out that unauthorised disclosure figures "will not all be related to customer data. Some may be internal HMRC data such as policy, guidance, workings/calculations, court proceedings etc".
As well as unauthorised disclosures, the total of 1584 incidents in 2018-19 cover a wide variety of circumstances including 66 cases of data loss through the post and three electronically, theft, loss of building passes and IT security.
An HMRC spokeswoman said: "We take all security incidents seriously and ensure that lessons are learnt from all cases. If necessary, investigations will be carried out to improve processes for the future.
"HMRC has a strong security incident reporting culture. These numbers may appear high but in fact reflect the high awareness among staff of reporting security issues so they can be investigated with the aim of learning lessons to prevent recurrences."
It was announced in 2015 that all tax offices across Wales would close, with staff expected to transfer to new centres in Cardiff and Liverpool.
But it was subsequently decided that staff at a tax office threatened with closure in Porthmadog, Gwynedd would keep their jobs, with the office relocating within the town.
HMRC offices in Swansea, Wrexham and Cardiff will close in late 2020, and the Cardiff Regional Centre will open in November 2020.