Last year, a hacker demonstrated a prototype of a small USB device - the size of a small USB drive - that could destroy electronics into which it was plugged. Dubbed the "USB Killer," the device damaged electronics by sending a surge of power onto the data lines used to communicate.

Now a Hong Kong based firm - aptly named "USB Killer" - is offering such an eponymous device for sale. When the USB Killer is inserted into a USB port of a laptop, television, printer, or any other USB-enabled piece of electronics, it rapidly charges small capacitors within it from the USB power source to which it is connected. When the capacitors are fully charged (which can take less than a second), the device quickly discharges the power over its data lines - thereby sending an unexpected surge of power into the device to which it is connected. The USB Killer repeats this cycle as long as it is plugged in - but even the first discharge is likely to damage many electronic devices. (Note: The USB Killer website seems to be going down periodically - perhaps someone is trying to prevent the device from being sold.)

Security experts have long been cautioning about the danger to electronic devices posed by leaving USB ports uncapped. In the past we have focused primarily on the risk of someone sticking into a computer some USB device infected with malware -- and the resulting risk to information security - but, now, the physical risk once considered small, other than in the case of highly sensitive systems targeted by advanced attackers, may become widespread.

The makers of the USB Killer claim that their device can kill 95% of devices with USB ports - but Apple laptops are not included in the 95%. Apple, they say, has already implemented technology to protect its products - a security move that is certainly commendable.

It should be noted that future versions of USB C - still a fairly uncommon type of USB connector - may help address the risk of USB Killer device type devices by including functions that prevent unauthorized devices from connecting to the power or data lines of computers and smart devices; of course, that does nothing to protect the billions of devices already in the market, and also assumes that future security protocols cannot be circumvented or subverted.

So, what should you do now?

Don't leave laptops or other electronic devices unattended in places where someone intent on inflicting harm might be able to plug devices into USB ports. That has always been good advice due to the significant information security risks mentioned earlier - but, now, your physical computer may be on the line as well. You can also obtain and use a connector that disables access to the data lines within a USB port while still allowing charging -- these devices are sometimes known as "USB Condoms" - but, obviously, someone intent on harming you can pull the connector out of your device before inserting the USB Killer.

Of course, in the big picture, manufacturers should address the risk on a macro-scale. Hopefully, for example, laptop manufacturers other than Apple will start including protective technology in upcoming products, and mechanisms will be implemented to prevent unauthorized devices from connecting to USB data lines. In the meantime, stay vigilant.