Be warned - you might not get a job interview if your web profile is unappealing

Smarten yourself up. Everyone knows that this is what you have to do to get a job. Everyone understands that you have to proofread your application and scrub up well for interview. What many people don't yet realise is that there is a new imperative – you have to smarten yourself up online as well.

The huge growth of social networking sites over the past few years means that very many people now have some kind of online presence. And employers are beginning to take advantage of this to find things out about you that they would never dare to ask at interview and which you would never dream of telling them.

A survey of more than 220 HR professionals by Personnel Today and the law firm Charles Russell found that one in four employers are now using social networking sites to check up on candidates prior to offering them a job. And while some HR professionals are firmly against the whole idea, the practice is likely to become more widespread.

"Checking up on people's social networking profiles is still at an early stage," says Michael Powner, employment partner at Charles Russell. "But 25 percent of employers is a not insignificant proportion, and in some industries such as media, professional services and finance the proportion doing so rises to one in three. This is likely to be a going trend."

So what can employers find out about you? Even with the default privacy settings left on, anyone can have a look at your social networks. They can guess your age, be pretty certain about your ethnicity, look at your range of work friends, and so speculate about how well connected you are in your industry.

They can also make judgments about your online and real-world popularity, your sociability and even the kinds of people you hang out with. What would you think about someone with a lot of friends in consulting firms? How about someone with a lot of friends in the Army? Or someone in their early twenties who only has five friends? Keep your privacy settings open and a vast range of information becomes available.

This is more common than you might think. The graduate job site Milkround.com surveyed its members and found that nearly 20 percent of them continue to keep an open profile despite being in the middle of hunting for jobs, while a further 40 per cent only kept some aspects private.

Those who do opt to keep their profile open are giving an enormous amount of information away. Potential employers will make judgements about your politics, your sexuality, the extent of your family commitments, the appropriateness of your friend-to-friend banter, your attitude to narcotics and your religious belief. It may even be the fact that you don't even have the wherewithal to switch your privacy settings on that turns them against you. In short, leaving yourself this open will answer the first question that interviewers ask themselves: "Do I want to have this type of person in my organisation?"

If the answer is no, you are not going to get the job. And, given that social networking sites don't contain much work-related information, they are really only looking for information that will flag you as a problem. This makes a "no" much more likely than a "yes".

In the eyes of many HR experts, this means the practice is deeply flawed. "We would never advise any of our corporate clients to do it," says Michael Powner. "It's all unverifiable information, and they are opening themselves up to dabbling in prejudice and stereotyping: the very things that anti-discriminatory employment legislation aims to avoid. Good recruitment should be about asking whether you can do the job, not about making unverifiable assumptions about whether you will fit in."

But Powner adds that it is equally important that job-seekers realise that social networking sites are not private or semi-private spaces. "The internet is a public space, and employers have a right to look if they want to."

Mike Barnard, website and communications executive for Milkround.com, agrees. "Those with an open profile should consider how it might be viewed should they go to interview, and perhaps they should up their privacy settings as soon as they start applying for jobs," he says.

Because employers are going to be looking at you online anyway, there is something else you could do other than to simply lock down your privacy settings. You could create a professional profile on a site such as LinkedIn or an online CV on the likes of iProfile. That would give them something else to find instead.