People donating to the UK's tsunami relief fund have been warned by police to remain vigilant to bogus collectors trying to cash in on the disaster.
The UK public has so far donated £100m to help tsunami-hit areas
Crooks are trying to find out people's financial details by sending e-mails asking for money, the National Criminal Intelligence Service (NCIS) warned.
False websites purporting to be linked to charities are also spreading computer viruses.
NCIS said people should not be put off donating, but should be vigilant.
Meanwhile, the UK aid effort was boosted on Saturday when Chancellor Gordon Brown announced the government would refund VAT charges on all charity records and concerts raising funds for tsunami appeals.
The money would be donated directly to the Disasters Emergency Committee, the umbrella group of charities, he added.
More than 150,000 people have been killed by the Boxing Day tsunami in South East Asia, with the UN warning the death toll could soar as the fate of many thousands remains unknown.
Foreign Secretary Jack Straw said on Friday that about 440 Britons were either dead or missing in the disaster.
Press reports on Saturday suggested the final toll of Britons could be closer to 2,000.
The DEC, which has received more than £100m in donations from the British public, said any faxes or e-mails purporting to be from it were hoaxes.
Some of the e-mails offer to locate loved ones and ask for money to be deposited in overseas banks.
Oxfam received a bogus e-mail asking for a donation of £1.50 to be paid on a phone number that cost further money.
Scotland Yard said it was investigating a number of websites set up following the Indian Ocean earthquake.
Essex Police said bogus collectors had left envelopes appealing for cash at homes in the county.
Last Sunday, thieves stole a collection box from Salisbury Cathedral, Wiltshire.
In Berkshire, Reading man Julian Hodgkins, 37, is due to appear before magistrates on 14 January accused of taking money collected for tsunami aid.
Father-of-two Christopher Pierson, 40, of Ruskington, Lincolnshire, pleaded guilty on Monday to sending hoax e-mails to relatives of people missing since the tsunami.
He sent messages to people who had posted appeals on the Sky News website, in which he said their loved ones had been killed.
NCIS warned people not to respond to unsolicited e-mails or text
messages, not to open attachments from unknown senders and to donate only to recognised relief organisations.
A spokesman said: "We do not in any way wish to dissuade members of the public from donating money to the registered charity tsunami appeals.
"But we urge them to exercise vigilance in order to prevent and disrupt these and other possible criminal scams."
Hundreds of British Sri Lankans were expected to gather in London's Trafalgar Square on Saturday to pay respects to over 30,000 people who lost their lives when the tsunami hit the island.
The Association of British Travel Agents has said that the majority of holiday resorts hit by the tsunami will be ready to welcome tourists again within weeks.
NCIS can be informed about any suspicious activity at the following email address: firstname.lastname@example.org