Help - Forum Being hacked?

[lfpm]

Our Forum is being hacked or something?

Many members, without their knowledge are posting a smile which includes somekind of a link, anyone who opens that page, a popup appears and asks for the username and password, the popup location is on another site and when the members insert their username and password, the other site is getting them:

Here is an image (forum.tayyar.org is our forum url, while alhms.com is the site that is hacking us?)



This is the smile that is appearing in many threads and PMs by the members (the members are not aware that they are inserting it)



The smile contains this link: http://www.alhms.com/jz/smile.gif (click on it and the pop up will appear)

Any idea what is happening and how can i stop it?

Thank you