Several high profile cases of data loss have emerged in the last year
People need to take control of how much information about them is being stored by organisations, says the UK's data protection watchdog.
Laws to protect privacy are not being used enough, the Information Commissioner's Office (ICO) says.
It is calling on people to "stand up" and use the rights available to them under the Data Protection Act.
Visitors to the ICO's website can now use a Personal Information Healthcheck to help them protect their privacy.
The ICO says that, while people are becoming more aware of the dangers of allowing their information to fall into the wrong hands, many are not using the legal rights available to protect their privacy.
A survey of 2,020 UK adults conducted for the Information Commissioner's Office (ICO) in August found 95% of people believed their personal information was valuable and more than 70% claimed to routinely shred personal documents.
But another survey found that 44% had never considered contacting an organisation to find out what information it held about them - a legal right available to them under the Act.
ICO deputy commissioner David Smith said: "Sometimes people have no choice but to provide personal details to organisations.
"Yet the more information we provide, the greater the risk that it will become out of date, be held for too long, or fall into the wrong hands.
"It is time for more people to stand up and use the rights they have under the Data Protection Act."
The online ICO Personal Information Healthcheck consists of a multiple choice quiz which asks where visitors store their information, and who they give it out to.
The aim is to pinpoint how vulnerable people might be to a breach of their privacy - and to suggest ways of controlling access to personal information.
It advises that customers who ask for a refund should think carefully before handing over personal information.
"If the shop assistant can't tell you why your personal details are needed, then don't give them out," says the ICO.
Similarly, says the ICO, people should always ask if their personal details might be passed to a third party, or used for marketing purposes.
"If you don't want a company to pass on your details, always remember to opt out - or you may have to write to the company to ask for details to be removed from its database."
In the last resort the ICO advises customers to seek out another company if they cannot guarantee the unwanted use of information.
The launch of the ICO's Healthcheck comes after several high-profile losses of sensitive data by government and private organisations.
"These losses demonstrate the risks if too much personal information is kept," says the ICO.