I think we all already know but just in case

Some users put links on the wall that are false, contain virus troyan

example wall of admin joto
http://dispenser.tf/Joto

for new traders never click this link of wall

edit: joto have 3 negative votes,people are incredible

Yes it's those links that downloads a .scr file which contains virus. I have received a lot of them on Steam too. Every shop owner please kindly delete the comment on your wall if it is spammed with such links.