Net Lingo give the most complete description I have seen so far for Digital Dirt:

Unflattering information or opinions that you may have written on blogs or in chat rooms that could come back to haunt you, for example in a job interview. “Digital dirt” also refers to unflattering information that someone else has correctly or incorrectly written about you that can be found on the Internet, usually on social networking sites.

To give an indication to what degree employers consider a job applicant today by their social media profiles you should read this article on Workopolis:

Here’s what employers say they least want to see in candidate social profiles:

• 83% of employers say they are turned off by references about using illegal drugs. (If this comes as a surprise to you, it’s definitely time to cut down on the illegal drug use).
• 71% are turned off by posts of a sexual nature. (Nobody wants to see that).
• 65% are turned off by use of profanity.
• 61% are turned off by bad spelling or grammar.
• 51% are turned off by references to guns, and
• 47% are turned off by photos of consuming alcohol.

Only a few months ago, a friends son, just qualified to drive and I’m sure normally a law abiding good citizen received a speeding ticket, he immediately posted a comment on Facebook describing the arresting officer using unflattering slang and specifically describing him as a well-known farm animal, the irony is he has every intention of becoming a police officer himself. Luckily it was brought to my attention and I explained to him what digital dirt was and how it might affect his chosen career.

These self-inflicted forms of digital dirt on social media are very easy to clean up, when you “grow up” you can just delete the accounts or go through every post and delete the offending ones, of course you can’t go correcting bad spelling and grammar. There is always the risk that someone else has “retweeted” the offensive comment, or that they have screen grabbed and shared it themselves. You can always ask them to remove it? But then it might have been intended to be malicious.

The above articles only really covers social media, but there any number of blogs you might have commented on or someone has mentioned you, that’s has to be approached in a different way. I worked on a case a few years ago where a graphic designer tried her hand at “web design”, she may have been very creative but her technical skills were lacking early on, one of her first clients took it on himself to post very nasty and career destroying comments on dozens of forums and blogs naming her using his anonymous profiles. A pleasantly worded standard email with links to a couple of her successful works to a few of the blogs requesting they remove the posts got rid of most of them, in fact the only ones that didn’t respond were on either abandoned blogs or busier forums, burying the remainder with some positive posts did the trick.

There are websites like BrandYourself who help you first by making you aware of what pages are out there who mention you and then suggesting ways you can “bury” any unflattering content by creating profiles on multiple social networking sites, I suspect their free option would bury the digital dirt that most teenagers these days seem to be accumulating, that they will later regret. the only thing that worries me about this approach is that it neglects images which will still show up in search results, but I would guess that opening an account with any number public image libraries and uploading a few complimentary pictures maybe altered using an iPhone app, tagged with your name, even fairly obscure libraries would do, for instance shadowness and worth1000 or the popular flickr and pinterest sites would do.

Burying Digital Dirt can be considered very similar to an SEO exercise, the technique used by companies to control the online traffic they receive, so lots of tips can be learnt from SEO sites, which there are many around where people discus how to manipulate what search engines see being the approach. Burying digital dirt can take months or even as long as a year, so if you’re in your last year of school or thinking of a career change, it’s never too early or too late to get started.