HM Revenue and Customs (HMRC) has issued a warning about fake e-mails about tax refunds which are designed to steal personal information.
HMRC said about 20,000 such messages were sent out in the week before the self assessment tax return deadline on 31 January.
The fake e-mails tell people to apply for tax refunds by filling in an online form that asks for bank account and credit card details.
"Anyone providing their details would have their accounts emptied and credit cards used to their limit," HMRC warned.
A similar scam reported in 2009 used a fake HMRC site hosted in Denmark.
HMRC said taxpayers who are due for a refund are only ever contacted in writing by post, not by e-mail, telephone or through external organisations.
Taxpayers should forward suspicious e-mails to email@example.com before deleting them.
Anyone who suspects they have been a victim of a scam, should report it to their bank immediately, HMRC said.