SAN FRANCISCO (KRON) — Malware on ATMs could be stealing your personal information, as thieves are installing programs on cash machines–and there may be very little you can do to stop them.

On Monday afternoon, KRON spoke with a security expert who said that this is just one of many threats facing ATM users. In the past, KRON talked a lot about skimmers that attach to the outside of an ATM and steal credit card information, but this time, the threat is inside the machine, and victims may not know they are being targeted.

In an ongoing investigation, the cybersecurity company Kaspersky Lab said it has found a new version of an old malware program called Skimer that’s designed to corrupt an ATM’s software.

By installing Skimer into the machine, thieves can steal personal information, credit card numbers, and pin numbers.

Unlike previous versions of the malware, the new Skimer can hide undetected for months, quietly gathering data until someone enters an activation code. If the thief is only looking for some quick cash, Skimer can also dispense the ATM’s funds on cue.

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“And some lucky cybercriminal is going to stand there with a very, very big bag and collect the entire ATM full of cash,” cybersecurity expert with AVG Technologies Tony Anscombe said.

Anscombe said that because Skimer is software inside the ATM, there’s almost nothing that the average person can do to avoid it.

It falls to the owner of the ATM to protect his or her machine.

“You have to think of them as a PC. Make sure they are patched, make sure they have the latest version of the operating system on them, make sure you’re protecting the ATM network with good anti-virus software, so the malware is detected if something does try to insert it,” Anscombe said.

That being said, Anscombe also said that ATM users should not let their guard down.

There are plenty of other security threats that can be avoided simply by being observant.

“When we go to an ATM, we should always be conscious of somebody not looking over our shoulder–our pin number. If the machine doesn’t look in good order, or if it looks like it’s been tampered with, don’t use it. Walk to the next one,” Anscombe said.

Finally, experts also said that thieves can actually instruct this malware to self-destruct, leaving no trace that there was ever a threat.