As singles meet and match online, cyberdaters all begin with the same problem: initially at least, they know nothing about their virtual partners. In the real world, couples are usually introduced through mutual friends or family members who are then grilled for personal history and references. In the online world, that knowledge has to be gathered directly from the potential date - and those getting-to-know-you e-mails usually form the first phase of most cyber-relationships.

Occasionally however, suspicions are aroused. Lawyers who claim to be in their thirties let slip that they have 20 years' experience. Apparently perfect partners refuse to reveal personal details and say the relationship has to be kept quiet. Attractive women start sounding remarkably like men. Usually, those suspicions are enough to send the relationship straight to the recycle bin, but increasingly, thousands of users are choosing to have their doubts confirmed first with the help of a professional background check.

Linda Alexander is the owner of whoisshe.com and whoishe.com, Internet services that offer personal checks on online lovers. In the three and a half years she has been running the websites, the San Diego attorney says she has checked the identities and records of "thousands" of virtual love-seekers. In fact, she says, in some 60 percent of the cases, her clients' suspicions are proved correct. Marital status and age are among the most popular areas for untruths, and men and women, it seems, are equally prone to exaggeration.

"We find men who say they're 48 years old and they turn out to be 71 and women who say they're 33 years old and turn out to be 47," says Alexander. "It's all over the place."

For $39, Alexander's firm will carry out a basic background check, searching public records to reveal a person's name, date of birth and address history. For $75, the search will also include professional licenses, aliases, bankruptcies and liens, while an additional $45 will reveal details of the subject's criminal record, if one exists.

Citing some of the worst examples, Alexander explains how her firm discovered that a woman with children was dating a registered pedophile, that one client's partner had been arrested for firing a gun into a house, while another was communicating with a woman who was actually serving time in jail for manslaughter.

In each of the cases, the client was aware that something was wrong and wanted their fears confirmed before giving their partners the final push. "In most cases, they're already 'in love'," she explains. "They're just not going to break up until something smacks them in the face and says something's not okay."

In fact, the clients of background services are often not the cyber-daters themselves, but members of their families concerned about their loved ones' welfare. With many senior citizens using the Internet to look for a late love, worried children often ask companies like Alexander's to vet their parents' potential partners. According to Arthur Faram, President of CheckMate, up to a quarter of his clients are the families of online lovers.

For Linda Alexander however, the stories that her investigators turn up also ring a personal note. She started her business in November 1997 after meeting a man in a chatroom who claimed to be a widowed doctor. When a quick check failed to find a death certificate for the man's wife, she became suspicious.

"I asked several times what was going on and he always had an excuse. When I ran a background check, I found that the wife was alive and well and still living at home," she explained.

While Alexander broke off the relationship and chalked one up to experience, Carmen Lynn, President of DateSmart.com, was less lucky. In 1989, she was working for a private investigator, carrying out surveillance work in dark alleys and talking to clients caught in bad relationships. "At the time. I thought, 'How could someone ever get themselves in a situation like this? They must know better, have better judgment, should be able to make reasonable decisions.' Then I met someone, knew him for five weeks and married him five months later."

Lynn's husband turned out to be a con artist who defrauded her of $25,000. Their marriage was annulled after just three months. Six years later, recognizing a need for cyber-daters to date safely, she set up DateSmart.com to allow Internet users to carry out background checks on their online partners.

Like Whoishe.com, DateSmart.com also trawls public records to reveal a potential partner's past history, but rather than offering a complete package of checks, DateSmart.com gears searches to investigate the client's specific suspicions. "DateSmart is more like going to the doctor and saying 'it hurts here'," says Lynn.

Her 80 percent success rate has included a man who dressed up as a woman to fool an entire chatroom as well as the usual collection of wives whose deaths were greatly exaggerated.

According to Lynn, the motives for deception are often difficult to determine but can range from monetary gain to simple kicks. Although there are a number of warning signs that can suggest something isn't quite right about a relationship, the best advice is to trust your instincts: if something feels wrong, it probably is.

While the rates at which background services reveal dishonesty may seem remarkably high, the bad relationships aren't necessarily indicative of cyber-dating as a whole. Arthur Faram only reported a 5 percent turn-up rate, while Linda Alexander points out that background services are usually the last stop for cyber-daters who are already suspicious, but aren't quite ready to split.

"I have to think that many of the times that people contact us, they already have a sense that something isn't right," she explains. "You just have to use the same kind of common sense you would if you met someone in a bar."

As she points out though, love often leaves little room for common sense.