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

[RatedDanny86]

That last point is spot on, but running a quick scan isn't a silver bullet anymore. Rootkits love to hide deep in the kernel where standard consumer antivirus tools won't even look without a specialized offline boot scan.

[Ethan]

Modern malware doesn't always hog your CPU or pop up weird ads trying to sell you fake pills. Sometimes the quietest infections are the ones stealing your browser cookies and saved passwords in the background while your games run at full FPS.

[Reward Annie]

People put way too much faith in defender sometimes. If a system feels sluggish and fans are spinning constantly for no reason, trust your gut instinct instead of waiting for a glowing red warning box that might never show up.