The phone rings and when you look at the caller ID you see something very strange—it's showing your telephone number. Chances are your phone number is being "spoofed" by a scammer.
"This is just the latest tactic being used by illegal telemarketers," said Robert Siciliano, fraud expert with BestIDTheftCompanys.com. "They hope that if you see your own number displayed on the caller ID, your curiosity will get you to pick up the phone."
A phone fraudster might also do this hoping to beat the new call-screening services now being used by millions of people. These services, including Nomorobo, PrivacyStar, Truecaller and WhitePages, rely on blacklists of known robocallers and illegal telemarketers to help block unwanted calls.
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"A person's own phone number is not likely to be on the blacklist, so these telemarketers hope to beat the filtering software by spoofing that number," said Bikram Bandy, head of the Do Not Call program at the Federal Trade Commission. "Fighting illegal telemarketing calls is a cat and mouse game and these telemarketers aren't giving up easily. We didn't think they would."
Aaron Foss runs Nomorobo, a free robocall-blocking service for land line phones. He figured out the new spoofing tactic after getting thousands of calls from Nomorobo users.
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"I ran the data and you can see a marked increase in these calls every month since the beginning of the year," Foss said. "These calls were getting through because the numbers weren't on the blacklist. We don't want to block good calls and who would call themselves?"
Nomorobo has now adjusted its call-screening algorithms, as have other similar services, to flag or block incoming calls that appear to be from that same phone number.
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At PrivacyStar, a free service to stop annoying telemarketing calls on wireless devices, they've spotted another new twist—spoofing the phone number so that it's nearly identical to yours, with only the last digit or two being different.
"They hope you will think it's someone locally calling and answer the phone," said Jonathan Sasse, PrivacyStar's CMO. "So from now on, when the call is from a number that is similar to yours, but off by just a few digits, we're going to alert the user to be cautious because this is likely a scammer."
The Better Business Bureau recently issued a scam alert about this caller ID spoofing.
"The best way to foil phone scammers is not to answer the phone if you don't recognize the name of the caller, if the caller ID says the number is blocked, or if it's an odd situation such as this," said BBB spokeswoman Katherine Hutt. "A legitimate caller will leave a message and you can call them back."
—By CNBC contributor Herb Weisbaum. Follow him on Facebook and Twitter @TheConsumerman or visit The ConsumerMan website.