1. The performance of computer is running slow.
First symptom of an infection by a malware on the computer is reduction in processing speed. The malware use a lot of resource for processing unwanted data.
2. Pop-ups spamming.
The malware will force the pop- ups ads to spam when user surfing over the web, clamming that Virus, Trojan horse or rootkit has been infected your computer, and the ads suggest you to download a free virus to resolve it. Beware, these is common method used by hacker and attacker which called as Social Engineering to trap the users to into malware trap.
3. Unexpected Crashes.
If the computer often crash or having blue screen problem, your computer has the possibilities which has been infected by the malware. The malware often hide itself together with the important files which in halt your computer from running properly.
4. Peculiar error messages.
If the computer continuously showing the error message, which stated that some of the programs or files in the computer unable to run, this might be another symptom of virus infection.
5. Anti-virus automatically disabled.
Most of the malware is designed to disable the antivirus once it as has been activated, so that the malware are able to runs in the background without being detected.
MALWARE ENCYCLOPEDIA 