Tucked behind your professional, yet pretty, profile picture, the descriptions of all your past jobs, and that column of "People You May Know" is a section of LinkedIn that most people have never heard of, let alone seen. And yet it's the real reason why you should actually care about sprucing up your LinkedIn profile and network.

Dubbed LinkedIn Recruiter, it's the company's flagship product and the core of the professional social network's Talent Solutions. Talent Solutions drive just over half of LinkedIn's revenue, $161 million in the last quarter. While any LinkedIn user can see jobs and the pages companies build for themselves, Recruiter is only visible to companies that pay to use LinkedIn as a candidate sourcing and hiring tool.

Recruiter is a bit like a two-way mirror where companies and recruiters can see all of your profile information, without you knowing they're checking you out. For example, recruiters can search for people with specific skill sets, flag them and add a dossier to their profile – all without that person knowing. They can all of the jobs they've listed and people they're watching. Sure, there is a "Who's Viewed Your Profile," but those using LinkedIn Recruiter can make themselves anonymous (as can paying LinkedIn premium account members).

LinkedIn wants to make sure those well-paying recruiters and companies have the best possible experience so that they stick around, maybe even tell their HR buddies. To that end, LinkedIn recently unveiled a refreshed Recruiter home page more in line with its consumer-facing products.

The Recruiter search tool lets recruiters search for specific types of people. Image: LinkedIn

"We've seen the impact that simplification has had on member growth and engagement," Parker Barrile, Senior Director of Product Management for Talent Solutions, tells Wired. "This new page is about bringing that same principle into Recruiter."

Recruiter is basically getting "Katyfied". The redesigned page features a new search tool, update stream, and section called "People You May Want to Hire." Recruiters can more easily scour LinkedIn's network of 200 million and growing profiles and keep track of who they are considering for jobs.

To date, more than 16,000 clients or companies pay to use LinkedIn Recruiter. The list includes big names like Google, Facebook, Unilever, BP, and L'Oreal, amongst thousands of other large, medium and small business and recruiting firms. The average cost per recruiter account is about $8,000, and it goes way up from there depending how many HR folks are hammering away on it. Suffice to say, even with volume discounts, the companies who have thousands of recruiters are paying a hefty amount for LinkedIn's tools.

It's easy to see what LinkedIn is doing here. The more it improves Recruiter, the more the service becomes money well spent. Happy recruiters mean more and more recruiters using LinkedIn, which in true network effects fashion translates to LinkedIn becoming the future of hiring (not to mention the fatter future of LinkedIn's revenue stream). By design it's going to be very hard for anyone else to catch up.

Recruiter already offers several unique features that are incredibly hard for companies to build or find elsewhere: a giant data set of more than 200 million users and growing, a way to engage passive employees, and the ability to build career branding around a company. The value of the LinkedIn's data is clear – it would take companies years and years to build a candidate pool even a fraction of that size, and it would be nearly impossible to keep up to date.

The company has already dropped a "nuclear bomb on recruiting," according to Ed Nathanson, director of talent acquisition at security software company Rapid7. Nathanson says that Rapid7 now uses LinkedIn Recruiter for all of its recruiting purposes, and that the company's recruiters spend anywhere from four to five hours on LinkedIn each day. He and his team have used LinkedIn to more than double the size of Rapid7 in the last year and a half.

In other words, Nathanson finds the vast majority of future employees on LinkedIn. And if you aren't on LinkedIn? He'll probably never find you. And even if he did, he probably wouldn't hire you. "I'm always amazed at people who aren't there now," Nathanson says. "When I talk to candidates and they aren't on there that's a big red flag for me."

Let that sink in for a moment. If you care a whit about your career not only do you have to be on LinkedIn, you should have a detailed profile with your job history. It should look like your resume. Taking advantage of LinkedIn features like Skills can also make you more searchable to recruiters. And of course, build out your network with people you know.

An update stream feeds recruiters the latest news of people they are following and potential candidates.

You don't even have to be looking for a job right now for LinkedIn's Recruiter to impact your career. The ability to source passive candidates, people who are not actively looking for a job but might be the most qualified, is incredibly valuable to LinkedIn Recruiter users. Instead of sticking to the usual job board or paying an outside agency to find candidates, recruiters can use LinkedIn to find exactly who they want with the skills and experience they want. Diane Hughes, the head headhunter at financial services company Northern Trust, says that LinkedIn is the best place to efficiently find high-quality candidates. "It's quality, it's quantity, and it's speed for me," she says.

LinkedIn's messaging service, InMail, gives recruiters the ability to contact anybody that piques their interest. But even if they don't decide to send an InMail, recruiters can still watch and receive updates on potential candidates. They can add the people to hiring "projects" and see who else in the company is tracking that person. There's even a new beta feature that allows a recruiter to see people within her company who can provide feedback on a potential candidate, all before the recruiter even gets in touch with that person.

It would be incredibly creepy were it not for LinkedIn's laser-focused mission on connecting the world's professionals and helping them be more successful and productive in their careers. You're putting your information on LinkedIn to be looked at, to help you get a job, if not now, at some point down the road.

"Our mission is to help people hire and I think it's easy to lose sight of that and simply focus on helping people find profiles," Barille says. "But that's only one step in the hiring process. This is about broadening Recruiter from just a tool to search and look at profiles to something that helps you discover new talent, but also drives much deeper into the recruiting workflow."

Going forward, LinkedIn will likely add more features to address this goal. Hughes says that she wants LinkedIn to add more features to source internal candidates, receive and track employee referrals, and a more fully developed applicant tracking system. The vision: LinkedIn as not only her top recruiting tool, but the only one.