Those who share personal details on blogs and social networking sites should remember that their writings will stay “on the record” for a long, long time to come. Jigsaw Data, a company which encourages users to buy and trade business contacts, has attracted some harsh criticism. It has been called a “really, really bad idea”, “clever, but creepy” and a “stalkers’ paradise”. By the end of the year, 5 million people should be referenced on Jigsaw. Granted, anybody who was unwillingly entered into the database can change the parameters or even say “Never contact me”. Still, the onus is on them to take action to rectify a situation they never accepted in the first place.

Remember the uproar about the new Facebook features that let members keep track of their friends’ activity on the site in a news feed fashion? Hundreds of members joined in a rebellion that forced Mark Zuckerberg’s company to implement changes to better protect their privacy.

In the case of Jigsaw, a third party is trading somebody else’s personal data, a situation that can definitely feel like an invasion of privacy. But in most cases involving privacy issues on Web 2.0-type sites, it is the users themselves who are recklessly sharing the most personal of details with the whole world.

“When I speak to college-age students, I am astonished by their naivete,” says Karen Coyle, a digital librarian and a member of Computer Professionals for Social Responsibility. “They have a false sense of privacy. They should realize that everything they post will remain out there as a permanent cyberbspace record.”

Recruiters are reportedly availaing themselves of this trove of information. After all, it is easy to check if a job candidate kept a MySpace page where he chronicled his wild college days. In some cases, this freely available information answers questions recruiters can’t legally ask of a candidate. Teachers, insurance companies, spouses and even marketers might also be interested.

Even if the information is not easily accessible because it is password-protected, law enforcement authorities can subpoena the hosting site to gain access. “I know for a fact that Facebook has responded to subpoenas. Members are not generally aware of that possibility,” says Karen Coyle.

Once incriminating photos or statements are out there, it is practically impossible to take them back. Yet many are trying. Hint : It is no use contacting Google or Yahoo about it. If a third-party posted the offending material, distressed Internet users can go to the webmaster who may agree to take it off. But there is no legal obligation as long as the information is accurate.

The line between public and private is blurring and it is this generation’s job to invent new rules. “I know people who were on Usenet back in the 80s and wrote things that they find embarrassing now that they are CEOs. But it is still out there,” reflects Karen Coyle.

As sharing personal information has become easier and audiences have exploded, users have not learned to use more caution. The first rule should probably be to pause before hitting the enter key. “How will I feel if a future employer or my mother ever reads this?” is a good test. Not high-tech, but plain old common sense.