It’s almost impossible these days to use the internet without giving out some personal data. You can’t, for instance, make an online purchase without coughing up your card details. And all the little conveniences that make the web worthwhile require some sacrifice of online security. We all know by now that our bank will never email us to ask for our details, but where should you draw the data line? Here’s PC Advisor’s rough guide to what information you should, and should not, hand over.

Almost never provide:

Driving-licence number: Although the DVLA's site may require you to enter this information if you need a new licence or something similar, no other site should.

The police will need your licence to process traffic offences and so on, but they always prefer to physically see both parts of your licence in the flesh, as it were. The same applies when you hire a car.

National Insurance number: Using the online services of HM Revenue & Customs – to self assess your tax burden, for instance – will require your NI number. No other site should require it - contrary to advice given previously that credit-checking sites such as Experian require NI numbers. Instead, they need only your date of birth, full name and details of all the addresses you've lived in the past six years. Keep your NI number to yourself!

Hardly ever provide:

Bank-account number: Your bank will probably require this number when it sets up your online banking, as will any credit-card accounts you set up with automatic payments from the bank account. After that, no other sites should ask for or need this information. If a friend needs your details to put money in your account, simply hand over the final eight digits and your sort code.

Passwords: Only a site you’re logging in to should ask for a password. Don’t share one with any other site. Use a different password for each site and avoid using real words in your passwords. If the resulting smorgasbord of passwords becomes confusing, use a password manager such as Password Safe.

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Be careful about giving out:

Credit-card number: You can’t shop online without it, but be careful with sites that you don’t know by reputation. You could keep a separate credit-card account for purchases from sites you’re not especially comfortable with. Otherwise, use PayPal or similar secure transaction merchants.

Mother’s maiden name: This could be used, along with other data, to steal your identity. Some websites ask for this name to release your password if you forget it, but you should use other information, such as your school or pet’s name, for this purpose if the site allows you to do so. And avoid publishing this information on social-networking sites such as Facebook.

Home address: As with credit-card numbers, you can’t entirely avoid sharing your home address when you’re making a purchase, but do so only when necessary. Identity thieves find this sort of information really quite useful.

Date of birth: If bad guys get hold of this one, you can’t change it – no matter how much you might want to. Many websites that ask for your birth date will do so only for marketing purposes, in which case you can make up a date. Other websites will ask for it in order to verify your age for certain age-sensitive products.

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