Fraudulent phone calls from "your bank" warning of a problem with your account have been occuring for years. But recently, these caller ID cons have exploded — and been tweaked to appear more convincing in efforts to steal your money and identity.

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In the last six months of 2011, scammers made more than 1 million of these calls, according to phone-fraud watchdog Pindrop Security. Their frequency increased each month, with a 52 percent spike between July and December. In the con world, they're known as "vishing" calls — short for voice "phishing." Phishing refers to any of a wide collection of ruses that try to trick you into disclosing personal information.

You may have gotten one of these calls. You pick up the phone to hear an automated message or sometimes a person claiming that your bank or debit card account has been frozen or somehow compromised. Your caller ID screen reassuringly displays the name and number of your bank.

You're asked to either dial a callback number or to immediately provide account numbers, PINs or other sensitive information. Sometimes the come-on arrives as a text message.

With your information in hand, the scammers may then use another phone line to call the financial institution. This time, its caller ID screen displays your name and phone number, which makes the employee who answers more likely to fall for fraudulent requests to transfer cash or otherwise deprive you of your money.

It's caller ID "spoofing" — the bad guys use special technology to put whatever name and number they want on the screen of the person who's receiving the call. Spoofing software has long been available online for free or for as little as $5 per 25 minutes of calling time. It's legal, but the federal Truth in Calling Act, signed into law in December 2010, makes it illegal to use the technology "for the purposes of defrauding or otherwise causing harm."

Increasingly, say Pindrop and other security firms, scammers are using Internet-based phone services, which may allow callers to choose their area code and even the prefix number that shows on caller ID — no matter where they actually are.

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