How to find that our computer is attacked by virusus

 1.The computer will start slow comparing to its normal speed, some folder,browsers,or application will not
work properly when it selected.or it will close suddenly.
 2.The computer will automatically restart or there is a way for crash.
 3.The system will show errors for entering files or application etc.
 4.printer will not work properly.
 5.Some files and folders cannot be accessed. this shows some pop ups or some dialogue boxes with errors.these are some normal symptoms of viruses. virus scanners are designed according to their targets, thus it will find viruses according to their targets.but there are thousands of viruses created day by day.these types of virus are viruses are mostly spread through Internet,usb's etc. most of the viruses will hack our computer files and send them to hackers.so we should be aware of viruses.there are some top kind of viruses which we see mostly: Trojan,Trojan horse,worm,exploit
etc.