Vanessa here from AllClear ID. From your smartphone showing everyone where you’ve been, to your Internet surfing creating “cookies” that deposit themselves in your Web browser’s files, you may not know the extent to which your personal information – and how much of it – is being gathered.  Everywhere you go online, the sites you visit and what you see are all being tracked.

Tracking your behavior to figure out what you might buy isn’t new: direct marketers, like the ones that send you coupons in the mail, have been doing that offline for years. But the online world captures a big amount of your day-to-day activity, from socializing with friends to searching the Web. By combining the online and offline data, the amount of information marketers can determine about you is huge.

You can see how much is know about you online by looking – where else? – online. One detailed site is PeekYou, which shows your digital footprint by matching personal Web pages and blogs with Facebook, LinkedIn profiles, Twitter feeds, etc. The result is a vast array of information listed under your name (sometimes accurate, sometimes not), including your age, address, where you work and went to school.  The site also links to “public record” brokers, such as PeopleSmart, Spokeo and Intelius, which can provide even more personal information, like your address, contact information and photos of you and your home – all free of charge.

If you want to stop your computer from “stalking” you, there are also free tools and software that can eliminate, or at least limit the amount of information you share:

  • The best place to start is with your web browser. All browsers offer tools that let you block cookies. To change your privacy settings, hit the “Tools” or “Settings” button on your browser and choose a privacy level.
  • You can download free software from Abine or Disconnect.me which blocks “third-party” cookies that telegraph your activity to strangers instead of regular sites you frequent.
  • Many advertisers have joined a voluntary program that will search your system to tell you how many ad networks have planted cookies on your browser, and allow you to block some or all of them. If you want to opt out of advertising cookies, go to www.aboutads.info to find out how.
  • If you want to erase information from public data files, like the public record brokers mentioned above, you can opt out of them directly, or hire a serv­ice like DeleteMe, which gives you a tutorial on how you can do it for free, or  does it regularly for you for $99 a year

The downside of going off the grid: Many Internet functions are triggered by cookies, so if you disable them, some things simply won’t work. So sometimes you may need to flip the switch off to get some sites working again – and also remember to flip it back on when you leave.

Also realize that everything you do on the Internet could become public eventually. Even if a website you’re on has a strict privacy policy, these policies can – and do – change (Facebook’s annual privacy-changing uproar is a prime example). The best measure to take: Stop sharing data online that you don’t want to be public.