Want to break into a computer's encrypted hard drive? Just blast the machine's memory chip with a burst of cold air.

That's the conclusion of new research out of Princeton University demonstrating a novel, low-tech way hackers can access even the most well-protected computers, provided they have physical access to the machines.

The researchers say the ease of their attack raises fears about the security of laptop computers increasingly used to store sensitive information, from personal banking data to company trade secrets, to national security documents.

Freezing a dynamic random access memory, or DRAM, chip, the most common type of memory chip in personal computers, causes it to retain data for minutes or even hours after the machine loses power, the report found. That data includes the keys to unlock encryption. Without freezing, the chip loses its contents within seconds.

Hackers can steal information stored in memory by rebooting the compromised machine with a simple program designed to copy the memory contents - before the computer has a chance to purge sensitive data, according to the study.

Laptops left in hibernation or sleep mode, or simply not turned off at all, are the most vulnerable to the new type of attack.

Researchers have known since the 1970s that cooled DRAM chips can retain their contents long after power to them is extinguished, but the researchers said they believe their study is the first security paper to focus on the phenomenon.

National security agencies may also have been aware that the types of breaches outlined in the study are possible, the researchers said, but added they weren't able to find evidence of that in any publications.

The attacks were carried out by spraying an upside-down canister of multipurpose duster spray directly onto the memory chips, freezing them to minus 50 degrees Celsius, about minus 60 Fahrenheit.

One challenge faced by the researchers was the threat that booting the system will automatically overwrite some parts of the memory.

To make sure the contents were retained, they used small, special-purpose programs known as memory-imaging tools, which can be loaded over a network connection or a USB device, to save images captured from the memory chip. The attacks even work when the DRAM chip is removed and transferred to a machine set up by the hacker.

Tags: pc,computers,hackers,RAM,

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