When it comes to human resources and recruiting, some companies have best practices they don't necessarily want to bring to your attention. But as a professional, you should probably know these secrets about HR.

1. They have a 90-day new hire rule.

Years ago, when I first got into HR I was told, "Whatever behavior you see in someone's first 90 days on the job, multiply it by 10 and that's what the employee will be like in a year." New employees try to stay on their best behavior, but it wears off over time. That's why so many companies now have a "90-day clause" in the hiring contract, enabling them to fire you without explanation. It's so they can let you go if they see any behavior they don't like. Employers estimate losing millions of dollars annually on bad hires. The clause lets them cut losses faster.

2. They do "backdoor" reference checks.

Before hiring you, HR will check references. You may think you can control the process by giving names of only people who will provide glowing recommendations, but some HR folks also do "backdoor" reference checks. They tap into their own network of contacts and find someone who worked with you to get an unbiased viewpoint. In particular, this technique is used if it seems like you left your last employer under suspicious circumstances, e.g., you say you were laid off, but it sounds like you got fired.

3. They aren't afraid to go candidate phishing.

Ever had a recruiter contact you about a job and ask you a bunch of questions about who you worked with at a particular employer? You think the interview went great, but you never hear from the recruiter again. What happened? He or she was candidate phishing--aka getting names of people currently working at the company so they can recruit them out. Sadly, this happens more frequently to the unemployed. Why? Studies show employers prefer to hire people who are currently working.

4. You get labeled "high-maintenance" for being a policy enforcer.

Yes, the HR handbook was designed so you could reference it and stay in compliance, but it doesn't mean you should run to HR every time a co-worker isn't playing by the rules. Pick your battles. If an employee is doing something that could hurt the company badly, you should say something. But too many visits to HR about your peers and suddenly you'll be labeled as the one to keep an eye on.

5. They do whatever it takes to get you off worker's compensation.

Studies show the longer someone is out on worker's compensation, the less likely he or she is to return to work. People get disengaged and depressed when out on extended sick leave. They adapt to the lower disability pay rate and often never return to work. To keep this from happening, HR works with the employee's doctor and pushes to get the person released to do some kind of work--any kind of work, to make them come back to the office. Usually, they're given mind-numbing, boring jobs as a way to make them want to get better faster. They don't want you home on the couch feeling sorry for yourself. They want you at your desk.

6. They don't give references to avoid slander lawsuits.

The reason many companies have a policy against giving references is to avoid any slander lawsuits--especially in situations where the employee didn't leave on good terms. These days, companies are required only to provide dates of employment and pay rate. They can refuse to comment on an employee's performance. However, if asked if the employee is eligible for rehire, they can legally say "yes" or "no" and not be at risk of being sued. This is important, because if they say "no," then it tells the potential employer something went wrong. Thus, if you haven't explained honestly why you left your last job, it could be seen as suspect and you may not get a job offer.

7. Performance plans are HR's way of saying, "Start looking for a new job."

When HR puts you on a formal performance plan, don't expect to turn things around and become a star employee. What they're really saying is, "Get your resume out there and start looking ASAP." If you find a job sooner, they won't have to fire you and you won't go on unemployment. It's better for both sides because being unemployed makes it harder to get a job, which means you'll be on unemployment longer.

8. When it comes to layoffs, personality matters to HR.

When HR is told to complete a restructuring and cut a percentage of the work force, they consult with managers to choose who stays. While skills and productivity matter, personality is at the top of the list. Why? Layoffs create a stressful work environment. HR looks for employees who they feel will rally and do their best to stay positive. Those who have a history of being critical of the company and vocal about their frustrations to management often get let go.

9. A good performance track record won't save you from getting fired or laid off.

Don't assume that great annual reviews year after year equals job security. Those are just recognition for what you've been paid to do. On any given day, the rules can change and the company can decide they don't want to keep you. Past performance is not an insurance policy. HR is always thinking, "What are you doing for us now that saves or makes us enough money to justify the cost of keeping you?"

10. Online background checks are standard practice.

While some companies pay for formal background checks and are required to ask for your permission, the rest are (without telling you) doing free internet searches instead. If you have anything in your past that can make you a risky hire, HR will find it online.

Understanding the above can help you think through your own actions when working with HR and recruiting. Being prepared is the key. Also, it doesn't hurt to seek outside coaching from an expert to ensure you are making smart career moves. Knowing HR's agenda can help you navigate your interactions with them more effectively.