The reason why most computer malware are so deadly is because many users fail to recognize whether they have been infected or not. Had they detected the infection at an earlier stage, the damage caused could have been greatly reduced. As each virus is programmed differently, it becomes difficult to identify a virus outbreak. However, there are some general symptoms that make it easy to detect an infected computer.
Here are some of them:
1) Programs won't start or crash suddenly: If some system programs like the task manager or registry editor have suddenly stopped working or crash randomly without any visible reason, it is more than likely that your computer has got some form of worm that is attaching itself to various programs and thus, corrupting their code. A virus modifying registry entries to prevent these programs from running could also cause this.
2) Unusual Network Traffic: If even after closing your browser and other applications that may use the internet, you see that your computer is still downloading or uploading anything, then your computer is possibly infected with some form of spyware that is either downloading other viruses to your computer or is uploading your private information to a remote computer. In case you use a wifi connection, it is also possible that your neighbors are using your network.
4) Annoying Popups or Redirection to Strange Websites: If there has been an increase in the number of annoying popups while browsing the internet or your web browser redirects you to a different website from the one you wanted to visit, a virus or adware might be the cause.
5) Computer won't boot: If your computer has suddenly stopped booting, it is possible that some malware has modified your computer's system files. In such a situation, re-installing or repairing your operating system might be the only solution.
6) Slow Computer: Some viruses are designed specifically for this purpose. Malware programmers achieve this by designing viruses that increase your CPU's usage level to 100%. If on running the Task Manager, you find that your CPU's usage is constantly at 100% level, a malware might be the cause.