Blow air under the key(s) and press them both a few times, so if any sort of a tiny crud/solid object is stuck between the key and the contact point, they would either break off or move away.
Once you remember that you have done one of the above mentioned thing(s) to your keyboard, feel silly, and let all your worries about your “hacked” computer go away, because this is just a small issue where the Alt key is pressed down. I want you to retrace your steps, and try to remember if you either cleaned your keyboard recently, or sat on it, or fell asleep on it, or hit it because you couldn’t get a kill and your teammates roasted you. I usually don’t include this sissy step in any guides, but here, it’s necessary. Let’s get to it! Step 1: Assess the situation