You can never tell 100% if a computer is safe; however, there are multiple ways to protect a computer. One way is to update your computer. Most companies have what’s called patch Tuesdays. It allows the company to have a constant patch schedule and help keep a computer protected. Another example is having an anti-virus (AV) on the computer. Windows has one built into the operating system; however, its not the best on the market, but it will do the job. If you want to have even better security have a 3rd party well vetted company that specializes in anti-viruses like Bitdefender. These have more protection and better features to help protect your computer. Some of the features a 3rd party anti-virus are webcam and audio protection, ransomware recovery, website protection, crypto mining protection, and email filtering. Another way to protect a computer is not downloading random software off the internet. This is the biggest way to stop malware from being installed.
Some ways to tell if a computer does not have malware is by feel, scans from anti-viruses, cybersecurity hygiene, strong passwords, and baselines. Some malware will slow down your computer and can be felt by the user allowing them to run a malware scan and hopefully detect the malware on the system. Then scans from a AVs can detect malware that is present on the computer and remove them. However, the best is having good cybersecurity hygiene because you will implement all of the above to protect a computer. One method is not very effected; however, having multiple ways to protect a computer leads to a higher success rate of protecting a computer versus having just one way.
With there being no current way to 100% without a doubt tell if your computer is safe. People need to employ multiple ways to protect a computer to help keep it safe from malware. Without having multiple ways users leave themselves vulnerable to malware infecting the computer.