A selection of PortaPow USB condoms,also known as data blockers

Adrian Kingsley-Hughes/

There are three things that I make sure I do when I'm out and about. I seek out the best coffee I can find. I make sure I use a VPN when using public Wi-Fi,andI always make sure I use a USB data blocker, otherwise known as aUSB condom , whenever I use a third-party charger (such as those you find in coffee shops).

OK, first off, what on Earth is a USB condom? 

Also: How to use public Wi-Fi safely: 5 tips you need to know before you connect

A USB condom is a small dongle that adds a layer of protection between your device and the charging point you're attaching it to. 

Remember, USB isn't just a charging protocol, it also allows data to flow back and forth, andwhile most of the time this data flow is safe, it is possible to create a malicious charging port that can do bad things, such as plant malware on your device or steal your data.

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And it's not just chargers. Cables can also carry out all sorts of malicious activities. 

All these cables and dongles shown below can be used to do bad things to devices.

O.MG cables and dongles can be used to attack unsuspecting devices.

Adrian Kingsley-Hughes/

And don't think you can look at these cables and see the hacking wizardry inside -- you can't! They're so easy to confuse with other cables that I keep the little orange tag on them to prevent them from getting mixed up with my regular cables.

These "attack cables" are indistinguishable from standard cables, so much so that I have to mark them with an orange tag.

Adrian Kingsley-Hughes/

So, back to the USB condom data blockers.

Sold by PortaPow , these are a super-simple, cheap solution to the problem of using untrusted USB charging devices. Simply plug it into a port, and any and all potential data transfer between the charger and your device is severed, putting an air gap between the USB port and your smartphone, laptop, or whatever you are charging.

There are data blockers forUSB-A-to-USB-A , USB-A-to-USB-C , and USB-C-to-USB-C .

For the super-paranoid, there are alsotransparent data blockers , the idea being that you can tell if they've been tampered with in any way.

Transparent data blocker -- perfect for the super-paranoid (or just the really careful).

Adrian Kingsley-Hughes/

The job of the USB condom is simple -- to turn any USB port into a charge-only port by blocking all the data lines. Sure, you could make one yourself from a USB cable (slice it up and cut the data cables), but with these bespoke data blockers costing only about$7, it really doesn't seem worth the hassle.

Another company that makes high-quality charge-only data-blocking cables is StarTech. These cables are one meter long and come inUSB-A-to-microUSB , USB-A-to-USB-C , and USB-A-to-USB-A . These are priced around$12, all have a cutout on the USB-A port to show no data lines, and all are marked "power only.'

Also: My favorite USB-C accessory of all time scores a magnetic upgrade

Bear in mind: While a data blocker can prevent data transfer, the port might still be able to damage a device, either through accident, misconfiguration, or malicious tampering. For example, devices such as those fromUSB Kill can be used to, well, kill devices that are connected to them by sending high voltage through the USB port, frying the delicate electronics.

Nasty!

Data blockers can't protect against USB Kill attacks.

Adrian Kingsley-Hughes/

If you must use a charger, cable, or charging port that isn't under your control, it makes sense to use a USB condom. If you want an extra layer of protection, take your own charger or power bank (or a charger that's also a power bank, such as theAnker 733 ) with you and use your own cables.

See also

This$30 gadget claims to add years to your phone's lifespan. Here's howThis is the USB flash drive James Bond would useHow to strip wires like a pro (and my must-have tools)Stop! Your Apple charger may be a counterfeit, and this tiny gadget can tellThis$10 gadget is my favorite repair tool of all time

• This$30 gadget claims to add years to your phone's lifespan. Here's how
• This is the USB flash drive James Bond would use
• How to strip wires like a pro (and my must-have tools)
• Stop! Your Apple charger may be a counterfeit, and this tiny gadget can tell
• This$10 gadget is my favorite repair tool of all time