HMRC is warning taxpayers about an expected increase in the number of tax rebate scams sent during April and May 2019.
Legitimate tax rebates are processed by HMRC at this time of year, but fraudsters often take advantage of that by posing as the tax authority in scam emails or texts.
These ask taxpayers to provide their bank details in exchange for a payment, with the details usually collected through a fake government website.
In March, April and May 2018, HMRC received around 250,000 reports of tax scams, and made more than 6,000 requests to have fake websites shut down.
HMRC said young people who may have less experience of the tax system should be especially vigilant, and look out for the signs of a scam.
According to Ofcom, 95% of 16 to 24-year-olds and 51% of over-55s own a smartphone, through which they might receive scam messages.
Angela MacDonald, head of customer services at HMRC, said:
"We are determined to protect honest people from these fraudsters who will stop at nothing to make their phishing scams appear legitimate.
"HMRC is currently shutting down hundreds of phishing sites a month.
"If you receive one of these emails or texts, don't respond, and report it to HMRC so that more online criminals are stopped in their tracks."