Last February, my mother turned 62. Facebook, her favorite social networking site, turned 6. Their birthdays are two days apart, under an Aquarius moon, making them, by the laws of astrology, highly compatible. And while this may very well explain my mother’s affinity for the enormously popular site, I don’t think that’s it.

I suspect it has more to do with the fact that, every day, more and more of her peers are creating Facebook profiles of their own. As was widely reported at the time, between November 2008 and April 2009, Facebook’s fastest-growing demographic was women above the age of 55, which grew by an astounding 550 percent. Their male counterparts joined up, too, bringing the total number of users over 55 to roughly 6 million — more than the number of high school students on the site.

This is not your grandkids’ social networking site. And it’s not just social anymore, either.

What began as Facebook founder Mark Zuckerberg’s Harvard hobby has emerged as a pioneering leader of “Web 2.0,” the term that describes the rise of interactive, information-sharing applications aimed at facilitating connectivity and collaboration by the masses.

Indeed, in December Facebook revealed that its 350 million members — more than the population of the United States — were producing some 200 billion page views per month, outpacing both eBay and Wikipedia and gaining ground on Google, the long-reigning No. 1. For, these days, Facebook is more than a friend-finder or a photo album. It’s a powerful professional tool.

“Facebook is a business network,” says Time magazine’s Lev Grossman. “[After all,] what’s the point of networking with people who can’t hire you?” Grossman, a self-proclaimed “old fogy,” argues that far from the youthful game it once was, “Facebook has found its fullest, richest expression with us, the middle-aged.”

Perhaps. But is Facebook really the best place to put the office? To connect with clients? Sure, you can restrict access to personal photos with a “work profile,” and you can create a “vanity URL,” making it easier for people to find you. You can market your products by posting discounts on the “news feed” and you can research prospective contacts before hitting “accept.”

But for all its muscle — 500,000 applications and counting — Facebook is still, well, Facebook. While it and its more teen-populated competitor, MySpace, aim to be everything to everyone, hundreds of other social networking sites have specialized. In fact, there’s almost no industry or interest group without one: nurses have NurseLinkup.com; lawyers can go to Lawyrs.net; and creative professionals can congregate at Mediabistro.com.

And then there’s LinkedIn. Launched in 2003, the “business-oriented social networking site” claims 55 million members, approximately half of them in the United States. The rest are scattered throughout more than 200 other countries, including India, where the company says it’s growing fastest. It represents more than 170 industries and counts among its members executives from all of the Fortune 500 companies.

With what it calls a “gated-access approach,” LinkedIn puts an emphasis on privacy and aims to generate trust among users. Unlike the more egalitarian Facebook, where anyone can send a “friend request” to anyone else — provided that the person is searchable — LinkedIn users who don’t have a pre-existing relationship, such as a common employer or school, must be electronically introduced by a mutual contact.

So far, it seems to be working and, not surprisingly, the global recession hasn’t hurt. In fact, LinkedIn’s traffic more than doubled in 2008 as the newly laid-off swarmed its job boards, uploading millions of résumés and priming their profiles with positive recommendations. Meanwhile, employers were scouring the site for new talent; according to Socialnomics, another social media blog, 80 percent of companies use LinkedIn as their primary recruiting tool.

LinkedIn isn’t just about getting a referral or finding a job. Services like “Company Pages” allow users to explore organizations they might like to do business with, and “LinkedIn Answers” offers a forum for picking the experts’ brains. Yet it may be nothing more than LinkedIn’s mainstream status that accounts for the bulk of its appeal. As several connections told me, with so many people now using the site, your profile is your virtual business card; you should have one whether you’re looking for work or not.

If you do create a LinkedIn profile, be sure to adhere to online etiquette and fill it out fully, says Liz Ryan, Business Week Online’s workplace columnist, a former Fortune 500 human resources executive and an expert on the new millennium workplace. “A sketchy profile is impolite,” she says. “It sends the message that ‘I’m going to use this database to find people, but I won’t bother to include enough information about myself to indicate how I might assist anyone else.’”

Ryan’s other rules of engagement include refraining from cold contacting and overzealous outreach. “LinkedIn allows you to broadcast a note to your posse of contacts by way of a ‘Profile Update blast.’ Use these sparingly,” she says. It’s also important to make clear your intentions from the outset: “If you’re job hunting, say so. If you’re looking for investors, ditto.” While these may seem to state the obvious, new users often forget that meeting people online is no less real than off, and that the same rules apply.

There is, however, one big difference between the two: the security threat posed by virtual crooks and their crafty viruses, which have targeted users of social media sites and, according to the experts, will continue to do so in 2010.

That’s because social networks, with their ever-swelling ranks and infinite personal data, “offer cyber criminals a very good return on investment,” says Gerhard Eschelbeck, chief technology officer at the Internet security company Webroot and one of the world’s foremost experts on vulnerabilities and network security. Mirroring the growth of social media sites was an explosion of increasingly sophisticated malware, he says, “with cyber criminals using email to distribute malicious links and programming them near the top of search results for popular news stories.”

Last May, around the time that the microblogging service Twitter was hacked, Webroot published the results of a “risky behavior” survey of 1,100 social network users. Approximately a third said they include at least three pieces of personally identifiable information; two-thirds said they do not restrict any details of their personal profile from being visible through a public search engine like Google; more than a third said they use the same password across multiple sites; and less than half of respondents knew who could see their profile.

“Social networkers need to know who can see what information they choose to share, and how to spot bogus posts and emails touting ‘hot vaca photos of u,’” says Eschelbeck. “The key is user education.”

In response to the advent of new social engineering tricks used to fool users and harvest personal data, businesses have implemented new layers of protection for their office users. But, says Eschelbeck, as users become more mobile, that protection becomes more and more porous. “Accessing the sites via an unprotected wireless connection in, say, an airport introduces additional vectors for infection,” he says. And with so much personal information available, crooks can easily guess the answers to security questions in order to reset a password.

According to Ryan Naraine, a “security evangelist” at the Russian Web security firm Kaspersky Lab, vigilance is best. The ongoing Koobface attacks — against Facebook and MySpace and, to a lesser extent, Twitter — use a fake YouTube page that purports to be a video, says Naraine. “If the target attempts to view the video, he/she is prompted to install a fake Adobe Flash Player patch. But both fakes are easy to spot.”

In the event that your Facebook or LinkedIn account is compromised, it’s also likely that your machine is infected with malware, adds Naraine. “The first thing you should do is clean the machine using a fully updated anti-malware software. Once the machine is cleaned, it’s important to change your username and password and remove all references to malicious activity. And finally, warn your network of friends or contacts about the infection.”

Although the threat landscape is becoming denser and more complex, the good news, says Eschelbeck, is the security industry is stronger than ever and constantly innovating. “A prime example is the rapidly growing adoption of ‘cloud-based security,’ such as the Amazon data center model,” he says. “This is significantly strengthening security defenses for businesses as well as consumers.”

Writing on the Webroot threat blog, Eschelbeck predicts that “the cloud” will continue to grow: “This will be the next generation of the Internet; computing will become like a utility, similar to how we use electricity today. We will pay for what we use; the PC will become the visualization tool we look into for applications in the cloud. And more cloud computing platforms will become available as we capitalize on this economical, scalable model.”

While security threats are sure to remain and perhaps intensify, one thing seems clear: Social networking is here to stay, and for better or worse, business will be a big part of it. Whether it’s better or worse depends in large part on how you use it.