There are multiple different ways to tell if your computer is safe or not, but the easiest way is by checking your antivirus software and having it do a scan on your computer.  Personally, I use Avast because I have had good experiences with it, and it notifies me when it has filtered my mail to block potentially harmful content, blocks a website popup that could have contained harmful code, and many other safety measures that it takes. When the antivirus software does a scan on your computer, it might tell you what programs are at risk or what files on the computer could be damaging.  Depending on the software, it might also offer the capability to remove harmful files and malware from the computer to ensure that your files and your system stay safe.  There is also the option to set up incremental backups and defragmentation for your system.  I do these for my laptop because it is a dual function laptop for me, serving as both my educational laptop and a gaming laptop, so I like for my system to be the least cluttered it can be so that my games run smoothly, as well as ensuring there are no harmful files still on the computer. Another way to make sure your computer is safe is to monitor yourself and your activities on the web.  An antivirus software, again, can help with this by telling you when a link you click on might not be a good idea to click on. You also have to just be careful not to be tricked by social engineering tactics, such as phishing emails, so that you don’t compromise the integrity of your system.  An antivirus system cannot do it all, so self-monitoring is key in keeping your computer safe.  If you don’t expose your computer to potentially damaging content, you can be reasonably sure that it is safe.