Never write anything in your blog....

...that you wouldn't want to see on the front page of the paper in the morning.

This is old advice, dating back at least to the heyday of fanzines – about the 1930s to the 1990s. "Never put anything in your fanzine that you wouldn't want to see on the front page of the Times."

As technology has advanced, this warning has become equally apt for BBS postings, echoes, e-mail lists, and now blogs.

College student Michael Guinn thought the photos he posted of himself dressed in drag would be seen only by friends. But he made a mistake. And when someone showed the photos on Facebook to administrators at John Brown University, a Christian college in Siloam Springs, Ark., it was "the last straw for them," says Guinn, 22, who is gay.

In January, he was kicked out of school, his virtual paper trail of musings about boyfriends and visits to clubs a clear sign to administrators that, despite repeated warnings, Guinn's activities were in violation of campus conduct codes stating that behavior must "affirm and honor Scripture."

Michael Guinn just learned this advice the hard way. Other cases include:

In Costa Mesa, Calif., 20 students were suspended last month from TeWinkle Middle School for two days for participating in a MySpace group where one student allegedly threatened to kill another and made anti-Semitic slurs. The student accused of making the threat could face criminal charges and expulsion, says Bob Metz, assistant superintendent of the Newport-Mesa Unified School District.

An employer who was ready to hire a student from Vermont Technical College in Randolph Center changed his mind after seeing the student's Facebook page, says Lauri Sybel, director of the college career center. Since then, Sybel says she has checked other students' pages to make sure they weren't hurting their job prospects.

Face it. If you post something online, don't expect it to stay private. Even when services allow various forms of locking, such as Live Journal's friends lock, information will spread beyond the boundaries of your intended audiance.