Question: what are the most common symptoms of malware on a compromised system?
Answer: Slow computer. The most common symptom of a malware infection is a slow running computer. ... 
Blue screen of death (BSOD) ... 
Programs opening and closing automatically. ... 
Lack of storage space. ... 
Suspicious modem and hard drive activity. ... 
Pop-ups, websites, toolbars and other unwanted programs. ... 
You're sending out spam.