Updated

We've all been warned (and warned, and warned) not to respond to phishing e-mails, in which the bad guys pose as legitimate companies such as eBay or PayPal in an effort to obtain personal information and use it for nefarious purposes.

But increasingly, phishing attacks (search) may be coming from an unexpected quarter: online job offers.

Bill Greenblatt, CEO of Sterling Testing Systems (search), a provider of pre-employment screening and background checks for employers, says that many identity-theft con artists are contacting job hunters who have posted résumés on Web sites.

The thieves make a phony job offer and then ask for a Social Security number and birth date, on the pretext of filling out a job application or a form for a background check (search).

Greenblatt cautions job seekers that few companies, other than the big ones everyone's heard of, actually have online job application forms, because of the expense of setting up and maintaining them.

So if you're contacted with a job offer by a company you don't recognize, make sure the company actually exists.

Another red flag to watch for is a request for your birth date.

"Never give out your date of birth—it's an illegal question anyway," says Greenblatt.

If you accept a legitimate job offer, the company will need your Social Security number — but it should be encrypted automatically if you enter it into an online form.

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