The BBC reports that the number of "security incidents" across the five HMRC offices in Wales has almost doubled in five years.
Unauthorised disclosures - data revealed to the wrong people - has also doubled.
An 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.
Tax does have to be taxing.
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