Security Technology Explained

Is It Safe to Buy a Used PC? 5 Risks and How to Clean It Up Properly

Simon Batt 11-03-2019

Buying second-hand PCs is a great way to save some money. Unfortunately, they also come with their own unique set of risks you need to look out for!


Let’s look at some ways second-hand PCs can be more of a hassle than a help.

What Are the Dangers?

With second-hand technology, the overall quality always depends on how the previous owner treated it. As such, second-hand computers could have some nasty surprises lurking within from its previous owner.

Sometimes, malicious software is installed with harmful intent. Someone places malware onto the computer, then sells it to someone else. If the user doesn’t realize their PC has been infected, the previous owner can harvest them for information.

Sometimes, however, people have no desire to harm you directly. Instead, they may have practiced less-than-stellar computer safety and caught some viruses. They do a very basic clean-up before selling it to you, which means the viruses they caught still dwell within.

The Risks When Buying a Used PC

Let’s look at some ways a preowned PC can come with more than advertised on the seller’s listing.


1. Keyloggers May Be Tracking Your Typing

If the previous owner wants to monitor your internet browsing, they may install a keylogger to track your keyboard. This will relay everything you type back to the previous owner, including the usernames and passwords you enter into sensitive sites.

This method of attack is very hard, if not impossible, to notice occurring while you use the PC. As such, users can unknowingly give malicious agents their login details for sensitive websites.

2. Spy Software May Be Tracking Your Actions

The owner may go a step further and install software that tracks you. They could slip in malware that takes regular screenshots of the desktop to catch something sensitive. They may also add a program that uses the built-in webcam to watch you through the day.

This is a little more advanced than a keylogger, so the chances you’ll find a random eBay seller lacing their computers with high-tech spying software is quite low.


This would more likely be performed if the seller knew their computers were going to be used for lucrative business. As such, if you’re a business owner, it’s worth taking the extra step to ensure there’s no corporate espionage.

3. Cryptominers May Be Making Extra Money for the Seller

Cryptominers are a kind of software that mines cryptocurrency. Cryptocurrency mining requires processing power, so malicious agents like to install them secretly on other people’s computers. While the user uses their PC, the agent gains some extra cash by hijacking their processor.

What’s worse is that cryptominers go relatively unnoticed by the users of the infected machine. They may report that it has been “acting slow” as the processor redirects some of its resources to mining cryptocurrency.

You can learn more about crytocurrency hijacking (also known as “cryptojacking”) in our look at the top cybersecurity threats of 2019 The 5 Biggest Cybersecurity Threats of 2019 Revealed Concerned about online security and safety? You might be confident that your devices are secure now, but what about next year? Read More .


4. Illegal Deleted Files May Still Be Around

The previous owner may have downloaded illegal files to their hard drive, such as torrented movies. When they sell the PC to you, they delete all the files, thinking that’s enough to scrub the hard drive clean.

Unfortunately, deleting files doesn’t properly get rid of them. All it does is mark the file as available to be overwritten by other files. As such, if the previous owner deletes the files and then immediately sells it to you, the illegal files are still there.

Because the files are only marked to be overwritten, someone can restore them if there hasn’t been a lot of disk activity. If someone does some poking around within your hard drive before you’ve properly used it, they could find some incriminating files that would get you in trouble!

5. Malware May Be Lurking

Even if the previous owner was as innocent as they can be, they might have accidentally contracted a virus on their PC. This may still linger when they sell the PC onto you without them realizing.


If the last user didn’t properly wipe the drive, a virus may be dwelling in the hard drive of the PC. Even if they did wipe it properly, some nasty strains of malware can burrow into the BIOS, which makes them very resilient to antivirus.

How to Clean a Second-Hand PC

While these risks sound very scary, there are ways you can clean up a PC to ensure it’s safe to use. Let’s look at the ways you can give your PC a scrub to ensure nothing nasty is lurking inside.

1. Wipe the Hard Drive Before Using It

If you want to clean the hard drive, it’s worth doing a full wipe. This is a little more complicated than you may think. Not only must everything be deleted, but it also has to be overwritten with “junk data” to fully erase the files from the drive.

Thankfully, there are tools you can use to “nuke” a drive. This deletes all the files, then overwrites it with junk to ensure nothing lingers afterward. You can read how to do this in our guide to wiping a hard drive. How to Completely Wipe a Hard Drive There are two ways to wire a hard drive. Here's what you need to know to get it done quick and easy. Read More

2. Replace the Hard Drive Completely

If you don’t want the hard drive within the second-hand computer, why not change it out? Of course, this is dependent on how easily you can get to the hard drive—a laptop will prove much more difficult than a computer.

If you can swap it out, however, you can make absolute sure there’s nothing lurking on the PC by changing the drive. You can either get a new hard drive, or use one from your previous PC instead.

3. Flash the BIOS

If you want to ensure nothing bad is in the BIOS, why not flash it? Look up what motherboard the computer has, then visit the manufacturer’s site and download the most recent update.

Once installed, you’ll have a fresh BIOS that won’t have any nasty malware. You can read how to do this in our guide to downloading and updating a BIOS update How to Update Your UEFI BIOS in Windows Most PC users go without ever updating their BIOS. If you care for continued stability, however, you should periodically check whether an update is available. We show you how to safely update your UEFI BIOS. Read More .

New PCs Aren’t Necessarily Safer Than Used PCs

The risks may put you off second-hand computers, but you shouldn’t worry. As long as you’re careful with what and how you buy, you shouldn’t encounter any problems. After all, brand-new hardware can contain malware, too!

A few years ago, we saw the case of Lenovo selling laptops laced with malware Now It's THREE Pre-Installed Malwares on Lenovo Laptops For the third time in a year, Lenovo have been caught shipping customers computers laden with privacy-unfriendly malware, showing that they haven't learned the lessons from the public outcry over Superfish. Read More . Preinstalled malware is a major problem for users, as it abuses our natural inclinations that new hardware is always “clean.”

As such, you shouldn’t really consider all second-hand computers as unsafe minefields, just as much as you shouldn’t assume all new hardware is free of malware. As long as you take care with what you buy and clean it up properly, you should be fine with preowned hardware.

Staying Safe With Second-Hand Purchases

While second-hand purchases can include some nasty surprises, these are avoidable. By giving your PC a proper scrub before using it, you can be sure that it contains nothing sinister.

If you’d like to see some positives of buying second-hand computers, have a read on our guide to why you should buy used computers instead of new ones. 6 Reasons to Start Buying Used Computers Instead of New Ones Thinking about buying a new computer? Here's why a used, refurbished, or pre-owned PC might be a better option for you. Read More

Related topics: Buying Tips, Computer Security, Cryptojacking, Malware.

Affiliate Disclosure: By buying the products we recommend, you help keep the site alive. Read more.

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  1. westbend
    April 19, 2019 at 1:41 pm

    Is there a way to get the original OS back after wiping/or replacing the hard drive? Is there a way to do the wipe without killing the OS? Someone trying to save a few bucks isn't going to save that much if they have to go out and buy a new copy of Windows. Switching to Linux works but is not a good option for many people. A lot of systems come with a recovery partition to put the system back to its delivered condition (Bloatware and all). Is that normally enough?

    • Simon Batt
      April 19, 2019 at 2:15 pm

      Even better---there are ways to wipe the drive within the OS and tell it to keep itself around! We covered some ways to do this in our article here: //

    • Thomas Kainz
      July 11, 2019 at 10:11 pm

      Windows 10 comes with the ability to 'reset' the PC with the option to delete existing user data. When I buy a used PC - about 10 times a year - I usually take that option and once completed then do a secure wipe ('cipher' command from the command line) of all remaining free space on the drive. Of course, just for 'insurance' I do a full HD backup beforehand as a fallback but once the Windows reset and the free space wipe is completed and the PC boots up fine with no issues, there's no more need to keep that previous backup. Reflash the BIOS just to be sure and then do a good deep AV scan as icing on the cake.

  2. Zhong
    April 9, 2019 at 7:12 pm

    I'd say be careful with components that's falsely labelled and tried to lowball you with something that isn't or keep a dud.

  3. dragonmouth
    March 11, 2019 at 12:36 pm

    For at least the past 10 years I've been using nothing but second-hand PCs. Never had any software or hardware problems with them. But then I always either low level format the HDD or replace it with one of my own. Then I replace Windows with Linux. Couple of months ago I decided to treat myself to a more modern PC so I bought a refurb from one of the better known computer discounters. Within couple of weeks the PC died. I think I'll go back to using PC I pick up from the curb.