Families struggling financially are becoming a bigger target for identity fraudsters, according to a credit checking company.
Experian said there has been a 4% jump between 2014 and 2016 in third-party fraud attempts where the potential victims are low-income families.
It said this group makes up more than four million people in the UK.
Third-party fraud happens when criminals use a stolen identity to commit fraud.
Experian's data includes fraud relating to current accounts, mortgages, cards, savings and insurance policies and claims. The 4% increase relates to fraud which has been detected and stopped.
People in the "vulnerable" group increasingly being targeted are typically aged in their 20s and 30s, have very low incomes and may be unemployed or in low-skill and low-wage jobs, Experian said.
They often rent their homes from a social housing landlord and have very limited savings, investments, pensions or retirement provisions.
Experian said criminals recognise that struggling families may be likely to apply for credit more frequently and they are using this to their advantage by intercepting post containing people's new cards and Pins.
Households with high salaries and large disposable incomes remain another priority target for criminals, as do young professional families with children and mature families with older children, who continue to be fraud targets because of their higher levels of income, Experian said.
Nick Mothershaw, director of fraud and identity solutions at Experian, said: "Analysis of Experian data from 2016 shows that fraudsters are unscrupulous in targeting young people and families who are already under financial pressure.
"When a person makes a credit application, they are likely to receive information about the application, or a card and Pin, in the post. Fraudsters are intercepting this post, to gain control of the credit facility."
Experian operates National Hunter, a fraud prevention system enabling financial institutions to cross-match applications against more than 100 million previous application records to spot anomalies that may indicate fraud.
Here are some fraud prevention tips from Experian:
:: Always shred or destroy documents that contain personal information before throwing them away.
:: Never respond to cold phone calls or emails asking for account details, Pins, passwords or personal information.
:: Do not give too much away on networking websites. For example, pets' names or children's names could be used as passwords.
:: Register to vote at your current address. If you do not, thieves could use your previous address details to open new credit accounts, and run up debts in your name.
:: Monitor your post regularly so you know when to expect important documents - and when to act if they do not arrive.
:: Have your post redirected if you move house.
:: Always use secure, unique passwords for as many online accounts as possible, and ideally all of them. At the very least have a unique password for each type of service provider such as financial services, retail services and email.
:: Do not store account names and passwords on your smartphone, either in email, as a note, or to "autocomplete" when you open a website or app. It will be a goldmine for fraudsters if your device is lost or stolen.
:: Read all bank and card statements regularly to check for suspicious transactions.
:: Check for any applications or spending on your credit report that have nothing to do with you.