HM Revenue and Customs (HMRC) has lost computer disks containing confidential details of 25 million child benefit recipients.
Since the loss was announced on Tuesday, people have contacted the BBC News website with experiences of their personal information being put at risk.
IAN REDFERN, LONDON. PENSION DETAILS LOST
Three weeks ago I got a letter from the Inland Revenue telling me that they had lost a CD with my personal information on it.
I had contracted out of Serps (State Earnings Related Pension) and they were transferring the information to my pension company.
I wasn't very happy about it. They just told me I had got to be vigilant.
I shred absolutely every piece of information, and here they are losing my details.
I am very angry. What are they going to do if something happens?
They said they had launched an investigation, but couldn't even tell me when the CD went missing.
KATE CARRUTHERS, NEAR OXFORD. HER NATIONAL INSURANCE NUMBER WAS MIXED UP WITH SOMEONE ELSE'S
About two years ago I received some correspondence to do with National Insurance contributions and something didn't make sense about it.
When I looked into it, it turned out they had swapped my records with someone who worked for a huge corporation in Manchester and was on PAYE.
I was pretty much always self-employed before, and at that time I was not working and looking after children.
They sent me a form which asked me about my life history so, presumably, they could work out who I was again and allocate my number back to the right person.
I thought National Insurance numbers were unique - and I don't know where my details disappeared to in that time.
JOYCE HEWARD, BEXHILL, EAST SUSSEX. HER BROTHER WAS SENT FORMS WITH OTHERS' DETAILS
I was doing my brother's accounts and he received two letters from the Inland Revenue he shouldn't have received.
They had their personal details on them - name, address, telephone number, National Insurance number - everything you shouldn't have, or everything you should have to commit identity fraud.
I rang them up and spoke to a supervisor who said they must have got sent to the post room and sent together in error.
If it was my information, I would be jumping up and down.
I said to them they are the people at the top and we should be able to trust them.
We have been let down, basically.
ALAN HARDY, WIGAN. TAX CREDIT DETAILS CHANGED
In May I discovered that someone had changed my bank details with the Child Tax Credit office.
Someone had phoned up with my details to change my bank details to theirs so they could get my money.
I noticed just in time and I didn't lose any money, it seemed to have been dealt with by the office.
I didn't know how this person had got my details as I routinely shred everything.
But when the story broke of the details being lost I put two and two together and thought there's something wrong with the system.
It seems to me that security within organisations which hold personal details is very suspect.
A spokesman for HMRC said: "We are very sorry to hear of the problems your contacts have had. We apologise to them and their families for any distress caused by any errors on our part.
"We can't comment on individual cases but we are taking immediate steps to ensure this does not happen again."