International cyber-criminals are exploiting UK-based 070 personal phone numbers to defraud unwary internet users, security experts warned today.

Sophos said that the scammers typically claim that recipients of spam emails have been selected to receive a large cash prize, and that the fortune can be collected once the victim has revealed confidential information, including bank details.

In an attempt to reassure recipients that their lottery win is genuine, these emails often contain a contact phone number.

Sophos estimates that UK 070 numbers are the second most commonly used telephone numbers in these scams. US-based telephone numbers top the list.

Known as 'personal numbers', 070 numbers look like mobile phone numbers, but can be easily redirected to any number anywhere in the world.

In addition, 070 numbers can be acquired for free, as higher charges are paid by the caller to use them.

This means that anyone can quickly and cheaply acquire multiple phone numbers for business/personal/new friends, all of which redirect or divert to the same mobile phone or landline.

"Internet scammers are scooping up these free 070 personal phone numbers, redirecting them overseas, and posing as British lottery officials," said Graham Cluley, senior technology consultant at Sophos.

"They can easily cycle through a bunch of these 'throw away' numbers, using them to con innocent victims into revealing confidential information that can then be used to empty bank accounts and commit identity theft.

"The fact that these numbers are readily available has propelled Britain to a shameful second place in this scam chart."

Many new lottery scams using 070 personal numbers are seen each day. One recent example claimed to be a communication from the United Nations working with the World Bank, and indicated that $17.5m was ready to be released into the email recipient's bank account.

"With 070 numbers, callers have no way of determining where their call ends up, short of persuading the 070 service provider to tell them," added Cluley.

"They may think they are speaking to an official in London, when really they're on the phone to a scammer in Lagos.

"Everyone should be extremely suspicious of any email, fax or letter they receive telling them they have won a major prize in a lottery as they may be left with an empty bank account."