More than 180 websites responsible for income tax "phishing" e-mails have been closed down by the authorities in the past three months.
HM Revenue & Customs (HMRC) said the sites had been sending out e-mails enticing people to make tax reclaims.
In reality the scammers wanted people to hand over details of their bank accounts to steal their money.
HMRC said some fraudsters had become more brazen, phoning people at home and asking for their bank card details.
"Victims risk having their bank accounts emptied and their personal details sold on to other organised criminal gangs," said Chris Hopson at HMRC.
"We only ever contact customers who are due a tax refund in writing by post.
"We never use telephone calls, e-mails or external companies in these circumstances," he added.
In January, HMRC warned that "tens of thousands" of bogus e-mails, ostensibly offering refunds, had been sent out just before the deadline for submitting self-assessed income tax forms.
And last autumn the Revenue revealed that in September alone it had been contacted by 83,000 people who had received scam e-mails.
The HMRC's own website reveals that phishing scams are not restricted to fake tax rebates.
Other topics used by scammers to get a victim's attention have included the purchase of non-existent "anti-terrorist" certificates, child benefit and income support claims, compensation for being the target of a fraud, customs clearance for items allegedly sent in the post, and lottery winnings.