US security experts are warning consumers to be particularly vigilant when doing their Christmas shopping online this year.

The Federal Trade Commission and the National Cyber Security Alliance (NCSA) have published 10 simple tips to help consumers better secure their personal information.

Around 11 per cent of online shoppers intend to do 75 per cent or more of their holiday shopping online, according to a recent Forrester Research study, translating to $33bn in 2007, up from $27bn in 2006.

However, a recent McAfee/NCSA online safety study found that 78 per cent of US computers are not fully protected from hackers and cyber-criminals, and 64 per cent of Americans cannot determine whether a site is safe before visiting it.

"The Monday after Thanksgiving is known as Cyber Monday and it's the biggest holiday shopping day of the year," said Ron Teixeira, executive director of the NCSA.

"Last year, Cyber Monday online sales generated a record $608m compared to $457.4m on Black Friday."

An increasing number of Americans find it convenient and easy to do their holiday shopping online while at home or at work, but too many are letting their guard down, according to Teixeira.

"Cyber-criminals do not take a vacation during the holiday season, so it is important for shoppers to protect computers and personal information by following a few simple tips," he said.

The tips include thoroughly checking out the seller by doing some independent research before buying, always checking out return policies and knowing what you are getting.

Name-brand items at greatly reduced prices could be counterfeit, and legitimate companies do not send unsolicited emails asking for password or log-in details or financial information.

Look for signs that the site is secure, such as a closed padlock on the browser's status bar, install antivirus and anti-spyware software and a firewall, and use credit cards as a generally safe option to pay.

Shoppers should also print and save records of online transactions, and turn computers off when they have finished shopping.