We have a warning about those popular social networking Web sites. We've discovered online background checks are revealing embarrassing evidence that costs people new jobs.

MORE ON THIS STORY How To Clean Up Your Digital Dirt Warning From ExecuNet

KIRO 7's Graham Johnson investigated the consequences of "digital dirt."

Some of the big sources of digital dirt are Web sites popular with college students. They're posting very personal information and photos on Facebook and MySpace.

But it's not just their friends who see it.

"People have the most extreme pictures. It's like they almost go out of their way to get a real good Facebook picture," said one student on the University of Washington campus.

"A lot of crazy pictures and stuff," said another student.

"You know, what did you do this weekend, that kind of stuff," said a third.

We found all kinds of revealing photos on local Facebook sites. Many involve drinking.

There are huge beers, binge drinking with beer bongs and keg stands -- even a photo captioned: "Drunk walking home."

"Oh, you don't want to know what my best picture is. Oh, no, it's disgusting. My best picture is … just say underwear party," said Kurt Geater, a UW student.

Not exactly what you'd want an employer to see.

"It makes you look unprofessional to someone who's like interviewing you for a job," said Whitney Killian, a UW student.

Joseph Barrientos at Seattle University's career center warns a growing number of companies regularly cruise these sites when they do background checks on job applicants.

"Information is readily available out there and you want to make sure your potential employers see you in the best of light," Barrientos said.

To keep his students from losing jobs, Barrientos now hosts seminars on cleaning up digital dirt.

Finding it -- recruiters say -- can be as easy as typing a name into Google.

"I recommend considering technology and the Internet part of your public self. It's part of your resume. It’s an extension of your background," said Kristina Rusnak of Allen Partners Recruiting.

A survey by the recruiting network ExecuNet says 35 percent of employers who do online background checks have eliminated a candidate because of information they uncovered online. That's up from 26 percent last year.

"I do not know how someone could see a MySpace page with excessive drug use or partying and not have that influence their hiring decision," said Debbie Oberbillig of Allen Partners Recruiting.

MySpace and Facebook both offer privacy settings. In fact, I couldn't access many of the Facebook pages for the local students we met because I don't have an email address from their schools. But employers are finding a way around that.

"They do have what they call 'student ambassadors,'" said Barrientos.

Career counselors warn companies are now asking student interns or recent graduates with college email addresses to research their classmates.

"If employers are shallow enough to think that someone's fun little profile is a basis for whether they should be hired or not, then there's something wrong with that employer," said Josh Levine, a UW student.

But with employers now checking sites like these, here's what's going to happen to the photos of that underwear party:

"I'm going to have to delete that before I graduate I think," Geater said.

Even if you don't have a Facebook or MySpace page, if you're applying for work, experts say it's a good idea to know if you have any kind of digital dirt.