Make sure you run exactly one antivirus shield. Running two or more is even worse than not having one at all. That's because, instead of protecting you from malware, the programs will attack each other. So in addition to having no protection, your CPU and RAM will waste all kinds of resources for no good reason. I've even seen people running multiple AV shields have their PCs become so hot that their machines shut down.
When you run one AV shield, make sure it's set up to have an active shield, and to install new signatures and run scans at least once a week, at a time you know your PC will be running. It's still possible to get infected with malware when you run an AV shield. That's because your AV shield can only protect you against malware that it has signatures for.
Think of the signatures as vaccines. It's important to get your flu shot, and it'll protect you from certain strains of influenza, but it won't protect you from polio or measles. That's why it's possible to set up your AV shield to download new AV signatures. Keep in mind that the developers of antivirus programs can only provide you with signatures for malware they're aware of, so you're still subject to what we in the IT security world call "zero day" attacks. Even the best antivirus developers, like ClamAV or Kaspersky, will only have a signature for a new piece of malware as soon as the second day that it's been infecting user's machines.
But it's essential to run an AV shield, no matter what your operating system is, or whether it's a PC, server, or mobile device. A well updated AV shield will still protect you from 98 or 99 percent of infections. Just because people can still die in car accidents while using seat belts, antilock brakes and airbags, it's still important to use those things. They'll still greatly reduce your likelihood of dying or being seriously injured in a car accident.
And finally, as I've mentioned before, back up your entire hard disk partitions to local disks, or online ("cloud") in addition to local disks.
As Smokey the Bear says about forest fires, only you can prevent malware infection and spreading.
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