Criminals are able to camouflage the devices with legitimate card readers.
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"You're talking about money," San Jose State University professor and Cyber Security expert Ahmed Banafa told ABC7 News. "I mean, if they can get their money using any way or any means, they'll do it."
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Banafa explained these devices take seconds to install and depend on Bluetooth to later transmit collected data.
"Receiving a Bluetooth is not a difficult thing. There are devices that can just get that information. Once they store enough information- two days, three days- they can come back to the same location, download that information," he shared. "Whether they are in the back of a car when they go to the gas station, or maybe they are, you know, standing next to the ATM. And just download that information and look at what they gathered."
On Thursday, video uploaded to TikTok showed the moments after a customer claimed to have found a skimmer in Mill Valley.
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The Marin County Sheriff's Office confirmed it took a report about a device discovered at a Tamalpais Valley 7-Eleven. Officials plan to send the device to the Computer Crimes Taskforce.
In the last six weeks, at least six agencies across the Bay Area have issued warnings about similar crimes.
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On July 15, a device was reported at a Sunnyvale Chevron 7-Eleven.
Petaluma PD then reported skimmers and small cameras were found between a Bank of America ATM and three 7-Eleven stores.
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Oakland PD shared surveillance photos of a man planting a device in mid-July.
In August, a skimmer found at a 7-Eleven was reported by Broadmoor Police near Daly City on the 17th.
On the 19th, Morgan Hill PD was alerted to a skimming device and small camera above a Bank of America ATM keypad.
"Having your information, especially the financial information in the hands of the people who are not authorized to do it is risky all the time," Banafa added.
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He said crooks typically use the information to make purchases of their own, even order new cards, all on a victim's dime.
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"Don't use your debit card, use a credit card with a chip," he said. "Because the chip is more secure, it goes straight to the device instead of something that can read it and it's encrypted."
Banafa said to avoid skimming, consider paying in cash or using third-party options like Apple or Google pay, which won't transmit your credit card info.
"At the top of this, we'll look at the device itself. See if it is really tight or not, see the label, the seal that is available, look at the next device, ATM or pump, and see if it's similar," he suggested.
Take a few extra moments to protect your money.