Getting a new phone, tablet, PC or laptop for Christmas? Logging into Facebook or Twitter to tell the world? STOP. Install some antivirus software (for free) or you'll spend Boxing Day clearing up your mess. Also see: Best antivirus for Windows PCs and laptops. 

Here we explain how you can install one of the best-known free antivirus software programmes, AVG Free, on your Android phone, Android tablet, Windows PC or Windows laptop. We also discuss what steps you can take to protect a new iPad or iPhone. Also see: Do I need to pay for security software? 

Don't go online using a Windows PC or laptop without installing antivirus software on it. You are asking for trouble. It's all too easy to get a new computer for Christmas and, in your excitement, jump straight on to Facebook or Twitter to tell the world. Don't do it, or you'll spend Boxing Day clearing out viruses and other malware. Or, rather, that tech-savvy relative you happen to know will, and they won't thank you for it. See all security software reviews. 

How to install AVG Free antivirus on a Windows PC or laptop   

To download the free version of AVG Free just head to AVG's website and click the big green Free Download button. On the next screen again click the green Free Download button at the top of the page.

Free security Windows

The AVG_Protection_Free.exe file will automatically download to your PC. Launch the installer by clicking the notification at the bottom of your browser window or find the file in your Downloads folder.

Note that you will need to be an administrator to install AVG Free. If you are not using an admin account, ask the admininstrator to enter their password. AVG will then begin to install. 

On the first screen click Continue, then select Basic Protection and click Install now.

Free security Windows

When User Account Control pops up click Yes.

AVG will install itself and download new updates, then run in the background on your PC.

Free security Windows  

To run a scan at any time tap on the Protection icon on the AVG home page and select Scan now. You can otherwise leave it running in the background and forget about it. Also see: How to remove malware from a Windows PC or laptop.

How to install AVG Free antivirus on an Android phone or tablet 

Generally speaking you can get away without installing antivirus on an Android phone or tablet, but there are malicious apps to be found outside the Google Play store, and installing them is as simple as unticking a box in the Settings that lets you download apps from unknown sources. Plus, Android is now the most popular mobile operating system in the world and, as we saw with Windows laptops and PCs, that means it will become increasingly attractive to wrongdoers. Since AVG antivirus is available for free, you might as well play it safe and install it. Also see: How to remove a virus from Android. 

Launch the Google Play store on your phone or tablet. You probably have an icon for this on your home screen; if not, open the apps menu and look for what looks like a white shopping bag with a triangular icon on top. If this is the first time you've opened Google Play you will be prompted to accept the terms and conditions. You will also need to have already set up a Google account on your device (if you bypassed this when you first turned on the device, add a Google account in the Settings menu). 

With Google Play open, tap the magnifying glass search icon in the top right corner, type 'AVG Free' and tap the magnifying glass icon to search. Tap on the top result - 'AVG FREE 2016 - Android'. 

On the next screen you'll see more details about the app, including its user rating and some screenshots. Tap the green Install button, then press Accept to allow AVG to access certain features on your device. Once it has installed the green Install button will change to Open - tap this. 

How to install antivirus on new phone, tablet, PC or laptop

Before you can begin using AVG Free for Android you need to accept its terms and conditions, so hit Get Started on the first screen. You'll then be prompted to upgrade to the paid for version of AVG, which removes the ads. Don't do this unless you want to: the antivirus part of AVG is free. Just tap Continue With Ads to continue. 

How to install antivirus on new phone, tablet, PC or laptop

If this is a new phone or tablet, that's all you really need to do. By default AVG will scan your device once a week, although you can change this within the Settings, Protection settings menu.  

If this is an older phone or tablet that you're only just getting around to installing an antivirus on, hit the big orange Scan button. On the screenshot here you'll see AVG found a couple of threats, one of which is the fact we have it set to allow the installation of apps from unknown sources (necessary for sideloading apps from outside Google Play, but not a good idea if you're not sure exactly what you're downloading as it could be malicious). You don't need to blindly accept these warnings; just use your common sense. 

How to install antivirus on new phone, tablet, PC or laptop

To keep AVG running at the best of its ability, make sure you keep it up to date. Launch Google Play and click the three horizontal lines icon in the top left corner, then choose Settings. Under auto-update apps choose to either Auto-update apps at any time or to update apps over Wi-Fi only (if you have a limited mobile data plan choose the latter). From time to time you may still find an app update requests your permission, and this will be because it wants you to accept its updated access requests. 

Do I need antivirus on my iPad or iPhone? 

No. In general iPads and iPhones are considered secure, since Apple keeps a constant check on any apps allowed in its store, and claims to have built iOS with security at its core. 

But there have been vulnerabilities. Even if you haven't heard of previous iOS malware that has hit the headlines, for example WireLurker, Masque Attack and Oleg Pliss, we doubt news of the nude photos of Jennifer Lawrence and other celebs leaked as the result of an iCloud hack passed you by. 

These flaws have all been blocked by Apple - as have those that have occurred since - but in order to protect yourself from future attacks you need to ensure you install only safe apps and that all your logins are ultra-secure. 

The Oleg Pliss and nude celebrities scandals were a result of hackers targeting Find My iPhone and iCloud accounts, then logging in as their victims. You should always use a strong password for online accounts (see how to create a strong password), and avoid using the same login for multiple sites. 

WireLurker targeted iPhones and iPads when they were plugged into insecure Macs or PCs (read our instructions above on how to install AVG Free antivirus on your Windows PC or laptop). Only jailbroken devices were maliciously affected.  

On that note, jailbreak your iPad or iPhone only if you really know what you're doing. A good rule of thumb is to never install untrusted apps found outside the App Store, since Apple has no control of what goes on outside its walls. 

Finally, always keep your iPad and iPhone up to date. iOS updates are free to download and install, so there's really no excuse. If you're having trouble updating because you're running out of storage, just plug your iPad or iPhone into a (secure) PC or Mac and launch iTunes.

Follow Marie Brewis on Twitter.