Fraudsters are stepping up efforts to trick people into handing over their personal details by bombarding them with fake tax rebate emails.
HM Revenue and Customs has warned that almost 80,000 "phishing" emails were reported by taxpayers during 2012.
The taxman said activity tends to increase around this time of year because taxpayers have just sent in their self-assessment returns.
The emails, which often contain a link to a clone of HMRC's website, typically ask recipients to hand over their card and bank details, date of birth, national insurance number and their mother's maiden name in order to get a rebate. The details are then sold on to organised criminal gangs to commit fraud.
Gareth Lloyd, head of HMRC's digital security said: "HMRC does not email customers about tax refunds we only ever contact customers who are genuinely due tax back in writing, by post.
"If anyone receives an email offering a tax rebate and claiming to be from HMRC, please send it to firstname.lastname@example.org before deleting it permanently."
The revenue body said that last year it noticed a spike in the number of a phishing emails being reported after the self-assessment deadline.
HMRC took action to close down 522 illegal sites in 2012, which showed these emails originated from countries including the United States, Russia, Japan, as well as various parts of central and eastern Europe.
The emails often begin with a sentence such as: "We have reviewed your tax return. According to our calculations of your last year's accounts, a tax refund of (an amount) is due."
The self-assessment deadline day was on January 31, when a record 9.61 million people filed their tax returns on time this year.
Legitimate information about tax rebates will be sent out in the coming weeks, but this will arrive in the post and not on email. Genuine tax rebate forms, known as P800s, will never ask for credit or debit card details.
HMRC said the scam is a persistent one, with similar numbers of phishing emails having been recorded over the last couple of years, although the numbers will be the tip of the iceberg as many emails go unreported.
Anyone who receives such an email should delete it and report it, but must never try to reply, HMRC said.
The revenue body advises that anyone who believes they may have fallen victim to an email scam should tell their bank and card issuer as soon as possible.
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