Android phones and tablets can behave erratically from time to time, especially as the amount of junk installed on them piles up. Sometimes bad behaviour can be attributed to a virus or other malware, and it can be difficult to tell what's to blame.
Nine times out of 10 it won't be a virus causing your device to act up. They do exist, but they are rare, and are usually installed exclusively via dodgy apps. You'll find few of these if you stick to the secure confines of the Google Play store.
The most common symptom presented to us as evidence of a virus is dodgy pop-ups in the browser. Usually these can be removed simply by clearing the browser's cache.
Go to Settings > Apps > Chrome > Storage > Clear Cache. Within Chrome itself hit the three dots icon at the top right and choose Settings > Privacy > Clear Browsing Data, then tick all the options and choose Clear Data.
If your device is misbehaving in another way, the best way to rid it of whatever is causing the issue is a factory reset, which can be achieved via Settings > System > Reset Options > Erase all data (it might look a little different on some phones).
But this is not an attractive solution when you have it set up just how you want it, so you should be careful to ensure you back up anything important before you begin.
If you're pretty sure you know what's causing the trouble - perhaps it all kicked off after you installed an app that you're not sure is 100 percent trustworthy - then you can sometimes fix the problem just by removing that specific app.
Uninstalling an app can be difficult if it's given itself administrator rights, however, but following the steps we outline below you should be able to force it out. We'll explain how to put your Android phone or tablet in Safe mode, remove the administrator rights, and then uninstall the app.
Supposing you've done all the above and your device is still slow, consider that it may be a case of old age or a new software update that doesn't play nicely slowing things down. Check out our guide on how to speed up Android.
To prevent further threats, you might also want to install an antivirus app for your phone or tablet. You'll find our favourites in our round-up of the best mobile antivirus. Our top pick is Bitdefender.
If you're convinced that malware is at large, read on for instructions on removing it from your device.
Put your device into Safe mode
Put your phone or tablet into Safe mode. This prevents any third-party apps running, including any malware.
On many devices you can press the power button to access the power off options, then press and hold Power off to bring up an option to restart in Safe mode.
On other phones you hold down volume-down during boot-up to enter Safe mode.
If neither of these options work, Google 'How to put [your model name] into Safe mode' and follow the instructions.
When in Safe mode you'll see 'Safe mode' at the bottom left of the screen.
Now open your Settings menu and choose Apps. Search for the dodgy app in question, and if you don't know which app to look for just search for anything you don't remember downloading or which doesn't sound like a genuine Android service.
Remove the administrator rights and uninstall the dodgy app
Tap on the malicious app (clearly it won't be called 'Dodgy Android virus', this is just an illustration) to open the App info page, then click Uninstall.
In most cases, this is all you need to do to remove the virus, but occasionally you might find the Uninstall button is greyed out.
This is because the virus has given itself Device administrator status.
Exit the Apps menu and find the Device Administrators menu within Settings > Security. On our Samsung this is in Settings > Security > Other Security > Device Admin Apps. Here you'll find a list of any apps on your phone or tablet with administrator status.
Simply untick the box for the app you want to remove, then tap Deactivate on the next screen.
You should now be able to return to the apps menu and remove that app.
With the virus now off your Android phone or tablet, all you need to is restart the device to take it out of Safe mode.
Avoid future Android viruses and malware
• Don't install apps from outside Google Play unless you know what you're doing: This functionality should be disabled by default, but to check you can open your phone or tablet's Settings menu, go to Security, then ensure the Unknown Sources option is disabled. If you do install an app outside Google Play, be absolutely certain that you are installing it from a legitimate source and not a fake website posing as an official source
• Avoid cloned apps: 99 percent of the time you will be safe downloading apps from Google Play, but malicious code has been found within apps there. Avoid downloading what appear to be cloned apps from unknown developers, or apps that simply don't do what they say they do
• Check app permissions: No matter from where you are installing an app, check its required permissions before hitting Install. Never allow an app device admin permission, which prevents it being deleted. And does a video player really need to see your contacts? You can also check reviews online and browse the developer's website to see whether it's a genuine operation or cowboy business
• Keep Android up to date: The latest version of the Android operating system won't necessarily be available for your phone or tablet, but you should check that it is as up to date as it can be. Next time you upgrade, consider a brand that is known for its timely operating system updates. Check out our guide on how to update Android for further advice
• Install an antivirus app: You don't need to install antivirus on Android, but it can give you peace of mind if you're concerned about viruses, and the apps often have other useful functionality too. Be warned that Android antivirus is known to occasionally report false-positives, but if you know an app is okay you know an app is okay. Our favourite antivirus option for Android is Bitdefender, but there's also plenty of other options for mobile security software in this separate article.