Applicant tracking systems are the bane of legions of job seekers. These systems, which employers use to manage job openings across their enterprises and screen incoming resumes from job seekers, kill 75 percent of candidates' chances of landing an interview as soon as they submit their resumes.

The problem with applicant tracking systems, as many job seekers know, is that they are flawed. Very flawed. If a job seeker's resume isn't formatted the right way and doesn't contain the right keywords and phrases, the applicant tracking system will misread it and rank it as a bad match with the job opening, regardless of the candidate's qualifications.

The problems with applicant tracking systems beg the question: If they're so flawed and if they filter out good candidates, why do employers bother to use them? The answer is simple: Bersin says they still make recruiters' lives easier. Applicant tracking systems save recruiters days' worth of time by performing the initial evaluation and by narrowing down the candidate pool to the top 10 candidates whose resumes the system ranks as the most relevant. Even if some good candidates get filtered out, recruiters still have a place to start.

As long as employers rely on applicant tracking systems to screen resumes, qualified job seekers' only hope for passing through them successfully is to understand exactly how these systems work:

How Applicant Tracking Systems Rank a Resume's Relevance

Many job seekers and career experts think applicant tracking systems rely on keywords to determine the fit between a candidate's resume and a specific job. They do their best to identify keywords in a job description that may be important to an employer or applicant tracking system, then they stuff these keywords in their resumes.

In fact, what matters most to applicant tracking systems is the uniqueness or "rarity" of the keyword or the keyword phrase, says Ciampi. That is, the keywords and phrases must be specific to a particular job ad. Applicant tracking systems, which "see" all job ads a company has ever published, determine which keywords and phrases in a specific job ad are unique to that job ad, says Ciampi.

The systems then develop a ranking based on how closely a job seeker's resume matches each keyword and phrase and how many of the keyword phrases the job seeker's resume has, he adds.

What Recruiters See When They Look at Your Resume in an Applicant Tracking System

When a recruiter clicks on the name of a candidate whom the applicant tracking system has ranked as a good match for a job, the recruiter doesn't see the resume the candidate submitted. The recruiter sees the information the applicant tracking system pulled from the candidate's resume into a database, as the picture below shows.

Applicant tracking systems contain different database fields for information on a resume, such as a candidate's name, contact details, work experience, job titles, education, employer names, and periods of employment. These systems try to identify this information on a job seeker's resume, but if a resume isn't formatted according to the applicant tracking system, it won't pull this information into the proper fields. Some of it might be missed altogether, such as a skills profile or an executive summary, says Ciampi.

5 Tips for Optimizing Your Resume for an Applicant Tracking System

Job seekers can increase their resumes' chances of getting through an applicant tracking system by heeding the following do's and don'ts:

1. Never send your resume as a PDF: Because applicant tracking systems lack a standard way to structure PDF documents, they're easily misread, says Ciampi.

2. Don't include tables or graphics: Applicant tracking systems can't read graphics, and they misread tables. Instead of reading tables left to right, as a person would, applicant tracking systems read them up and down, says Ciampi.

3. Feel free to submit a longer resume: The length of your resume doesn't matter to an applicant tracking system, says Ciampi. It will scan your resume regardless of whether it's two pages or four. Submitting a longer (say three or four page) resume that allows you to pack in more relevant experience and keywords and phrases could increase your chances of ranking higher in the system.

4. Call your work experience, "Work Experience": Sometimes job seekers refer to their work experience on their resume as their "Professional Experience" or "Career Achievements" (or some other variation on that theme). "People get very creative on their resume because they think it will help them stand out, but in fact it hurts them," says Ciampi. "Often the computer will completely skip over your work experience because you didn't label it as such."

5. Don't start your work experience with dates: To ensure applicant tracking systems read and import your work experience properly, always start it with your employer's name, followed by your title, followed by the dates you held that title. (Each can run on its own line). Applicant tracking systems look for company names first, says Ciampi. Never start your work experience with the dates you held certain positions.

Meridith Levinson covers Careers, Security, and Cloud Computing for CIO.com. Follow Meridith on Twitter @meridith