By Dominic Casciani
BBC News home affairs reporter
Live marketplace: A criminal website selling UK identities
Internet fraudsters sell complete financial identities for just £80, according to an online safety group.
The details packaged and sold online include names, addresses, passport numbers and confidential financial data such as credit card numbers.
With six out of 10 people now managing finances online, experts say the public needs to do more to prevent e-crime.
The figure comes in data released as part of a week highlighting ways to protect identities online.
The Get Safe Online group, which is backed by police, government and banks, says ID theft is a serious problem because of an international trade in stolen identities and data.
Online marketplaces, often sited in countries with lax controls against e-crime, sell bundles of data harvested in concerted attacks against poorly defended computers in wealthier nations.
The safety group estimates that nearly half of all computer users in the UK are vulnerable because they are not using defensive measures such as a firewall, or up-to-date software which can identity malicious programs.
Crucially, warn experts, too many people use the same password for key websites, making it easier for bank details and other sensitive data to be gathered.
Criminal websites shown to the BBC by the Serious Organised Crime Agency were selling personal information for as little as £5 per piece of data or £80 for an entire package.
The data on sale at any one time typically includes names, credit card numbers and information in a card's magnetic strip needed to create working clones.
Tony Neate of Get Safe Online said fraudsters buying details online try to use personal information to make money as quickly as possible.
"Online criminal activity can be a sophisticated business, but each of us can take steps to prevent ourselves from becoming a victim," said Mr Neate.
"If internet users invest a relatively small amount of time and money in ensuring they are fully protected and up-to-date, the risk of such financial loss is almost negligible."
Banks say phishing attacks are rising - 10,000 alone in the first quarter of 2008.
These are typically emails which look like they have come from a bank - but in fact ask the recipient to log in to a fake website.
Nick Staib of HSBC said: "If your financial reputation has been compromised through identity theft, this could have an impact on your ability to obtain credit or borrow money in the future. Even with an explanatory note on your credit record, you may be viewed as high-risk."