This advice comes from the Association of Payment Clearing Services: 

• Make sure your browser is set to the highest level of security notification and monitoring. The safety options are not always activated by default when you install your computer. 
• Two of the most popular browsers are Microsoft Internet Explorer (use version 3.02 or higher) and Netscape Navigator (use version 3.03 or higher). If you have a difficult browser or use on-line services such as AOL or Compuserve, contact your ISP or software supplier to find out how to activate their security features. 
• Keep a record of the retailer's contact details, including a street address and a non-mobile phone number. Beware if these details are not available on the website. 
• Click on the security icon to see if the retailer has an encryption certificate. This should explain the type and extent of security and encryption it uses. Only use companies that have an encryption certificate and use secure transaction technology. 
• If you have any queries or concerns, telephone the company before giving them your card details to reassure yourself that it is legitimate. 
• Print out your order and consider keeping copies of the retailer's terms and conditions and returns policy. Be aware that there may be additional charges such as postage and VAT, particularly if you are buying from overseas always err on the side of caution and remember that it may be difficult to seek redress if problems arise. 
• Check statements from your bank or card issuer carefully as soon as you receive them. 
• Ensure that you are fully aware of any payment commitments you are entering into, including whether you are instructing a single payment or a series of payments. 
• Never disclose your card's PIN to anyone and NEVER write it down or send it over the Internet. 
• If you have any doubts about giving your card details, find another method of payment.