The user should be aware of the symptoms so that he will be able to detect a virus in his system. Your system will be running slower than usual. You will be getting lots of pop-ups. If all these problems are occurring, then it is possible that virus or malware or spyware has entered your device. Even if you have an anti-virus program installed on your device, your system can be infected with the virus. These irritating problems can be caused by other things as well. But it would be best to check malware.