How do I know if my PC has malware?

[TheRock]

Bit paranoid about this.

Are there clear signs that a system is infected, or can malware just sit there quietly?

Trying to figure out if I'm overthinking or if I should take it seriously.

[HitmanMatt53]

Both can happen.

Some malware is obvious:

Popups
Browser redirects
Unknown programs

Other types are silent and just use your system in the background.

Things to watch:

Unusual CPU usage when idle
Unknown processes
Slower performance for no clear reason

[error.404]

Running a proper scan with something reputable is always worth doing if you're unsure.