Online security matters
A cookie is a small file placed on your computer by a web site. None of your personal information, such as your name, address or credit card details, are held in your cookie. They are mainly to help keep track of online sales or services when using e-commerce websites like Amazon etc. This can be useful in helping the site remember what you have ordered and placed in your shopping basket, or remember who you are if you are entering a 'Member's Area'.
Buying goods online in a secure environment
The vast majority of reputable companies who sell goods online, who require personal information such as credit card details for e-commerce transactions, use high strength SSL (secure socket layer) encryption methods to protect sensitive information from being accessed. 128 bit encryption makes it practically impossible for unauthorised users to aquire this information. Sending this type of information over the internet is therefore perfectly safe, and any information kept in a database is always stored on a secure server in a secure environment, which is usually locked and well guarded.
In the unlikely event of unauthorised use of your credit or debit card (possibly by someone finding out your details in some other way) you must notify your card provider as soon as possible, in accordance with their reporting rules and procedures. The majority of banks and card issuers will either cover all the charges that result from unauthorised use of your credit or debit card, or limit your liability to £50. However if your bank or card issuer tries to hold you liable, some online shops will cover your liability up to a specified amount (usually around £50), if it is shown that the unauthorised use of your credit or debit card resulted from you using the card to make purchases from the companies secure environment, and not through any negligence by yourself.
It's normally a matter of course that reputable companies will take every precaution to ensure that your credit card information is secure by ensuring all of their pages requesting personal information are completed using a secure link and by utilising the maximum level of encryption allowed by your browser. You can check that you are shopping in a secure environment by looking for either a locked padlock icon or an image of a key in the grey bar at the bottom of your screen. This should appear on any page where you are entering personal information (such as your credit card details) - no other page will transmit information about you.
Ways to stay safe when browsing and shopping online