How do you know if your computer is being used as a spambot?

Your computer starts acting sluggishly and if you're on a messenger type program it'll spam people that you have added as friends.

Saying stuff like photo of me :"fake link that leads to a auto-downloading virus"

To fix:

Change your passWord for messenger based products

get a decent anti-virus and clean all problems found..

Don't be foolish and download 1001 things you find on the internet.