Faced with a would-be employee who had visited its offices under an assumed identity, loaded company information on to their personal computer and picked the brains of staff, many recruiters would be tempted to call in security. Fortunately for Alexis Kingsbury, PA Consulting's response was to offer him a job.

The reaction of the UK-based management consultancy is explained by the fact that the covert encounters took place at its virtual offices in Second Life, the computer-generated world in which people interact through alter egos known as avatars.

Kingsbury, who graduated from Loughborough University this summer, says that his virtual visits made him more eager to become a consultant and helped him to come across as knowledgeable and confident in his real-life interview.

PA's use of Second Life for recruitment illustrates how companies, as they shift marketing spending from print to digital media, are opening a new front in the battle for brains.

Changes in hiring practices, increasingly drawing on a global pool of talent, are hastening the trend, says Charles Macleod, PwC UK resourcing leader.

"The beauty of digital media is that it makes it possible to recruit internationally at a much lower unit cost," he says. Another attraction for employers is the prospect of creating a virtual window through which potential recruits can see something of the company's inner life.

Much of the investment has been aimed at strengthening the pulling power of employers' websites. As a result, modest careers sections are morphing into microsites bristling with tools for multimedia communication.

Allen & Overy, a City of London law firm, last year created a graduate site carrying profiles of recent recruits, blogs in which employees chat about their lives and a video documentary that follows lawyers and trainees as they wrestle with legal complexities. Replacing "very corporate, text-heavy" content with the voices of young lawyers has helped Allen & Overy get across its "personality", claims Zoe Gordon, graduate recruitment manager. There are, however, some thorns in the online garden. With the explosion of interactive media, recruiters complain they are under pressure to invest in the latest innovations - some of which will be quickly superseded.

"There is a great deal of noise in e-recruitment," says Deborah Self, recruitment manager at RM, the education technology supplier. "Often it is helpful just to ask your own people what they would find useful as job-seekers."

Yet most employers agree on the general direction of development. One coming trend, Self predicts, will see employers adding instant messaging to their websites, giving job-hunters the chance to chat with employees.

"We are trying to put ourselves in the position of a student," Macleod says, adding that by next year, students visiting PwC at careers fairs will be able to upload information from the company's stand direct to their phones.

The issue that most exercises large employers, however, is how to respond to the user-led boom in social networks. The ability of sites such as Facebook and MySpace to gather people together could create a golden opportunity for companies to reach young adults who might otherwise not come their way. However, as even the most enthusiastic social networkers would admit, the medium has a side that sits uncomfortably with business.

First, engaging in social networks can be a burden, since it obliges staff to respond to everyone who makes contact through the site. A second worry is that companies can rapidly be embroiled in public spats with detractors.

There is also the fear that users will take against businesses that muscle in on a territory intended for friendship. "We believe that social networks are about having fun, not recruiting people to become accountants," Macleod says.

Yet PwC is unusual in taking this stance. Social networks are now seen as central to the way in which young adults toggle between business and leisure.

"Many people run their life through online communities," says Alison Heron, recruitment marketing manager at KPMG. "If we want to talk to them about opportunities in professional services, we have to be in there too."

So if recruiters need a presence, what form should it take?

One option is to approach social networks commercially. In the US, Ernst & Young has created a sponsored membership group on Facebook for anyone interested in an E&Y career. Although identified as a corporate promotion, Ernst and Young's pages retain something of the spirit of social networking, leavening careers materials with photos posted by group members and opportunities to pose questions to E&Y employees.

More than 8,000 people have signed up to E&Y's group, showing that businesses will not automatically be shunned as gate-crashers. Nonetheless, the medium merits close evaluation.

The payback from sponsoring a corporate careers group on a popular social network is measured not by the group's ability to attract members, but by the number and quality of people who apply to the company. This raises the question of whether organisations could work their investments harder.

For years employers have financed clubs and societies at universities as a way of gaining access to students. Now, many of these associations have a presence on Facebook, creating a channel that could be linked to the corporate backer's website or, better still, an invitation for students to meet a company employee or campus ambassador.

"It could easily be done via a click-through advertisement or simple logo," says Ben Hart, chief executive of Glass, a digital communications agency, "but it's not something that, so far as I'm aware, companies are exploiting."

In the days before online communities, talent-hungry companies devoted themselves to a few well-chosen campuses. In the future, the prizes will go to employers who marry a deft personal touch with the reach of virtual networks. PA Consulting was drawn into recruiting in Second Life after setting up a virtual marketing presence there.

During working hours, prospective recruits are greeted by PA staff, fronted by avatars and directed to a multimedia recruitment suite stocked with careers information.

In December, recruitment manager Tim Symes hosted a virtual meeting for graduate applicants and PA managers. Through Second Life, would-be recruits used instant messaging to chat, they heard live presentations and questioned PA staff. While PA will not replace face-to-face methods, it now plans to repeat the event on a larger scale with experienced recruits.

As a professional recruiter, Symes highlights the "removal of geographic boundaries" and the ability to make "anonymous" contact during the initial phases of hiring as points in Second Life's favour.