A way you can tell your computer is safe is keeping it lock if it is not being use as the moment. And with that you have to come up with a password that you think nobody can guess but not too hard of a password being you have to be able to remember it. Another way is staying away from weird websites and not clicking on pop up ads that might pop up on your screen. Do not go to anyways websites your not use to clicking on because you might get a virus. Do not download any where file no matter what because if you feeling weird about download and scared it might be a virus then most likely it is. Do not let others use your computer so much or maybe at all because it a lot of personal information on the computer and it may lead to find out you password to your computer some how. If anything strange is happening to your computer and any way or you just questioning your computer go to where you brought the computer from and ask question about the issue. Or you can just simply get a new computer just for safety reasons and get rid of any personal information on the old computer. The issue can be your computer is slowing down but have nothing to do with the wifi, files going missing out of no where, a lot of pop up or very little pop ups, and also very hard time turn off the computer or even turning on the computer. There are many more computer issues out there but these are some main issue. So if you do not have any of these issues then your computer is more than likely safe and safe to use.