Advertisement Robots Instant Messaging me?

I've been getting so many IMs from what it says to be my friends but its obviously not. they say "hey come check out the pictures i put up of you here" and "click here and come look at my new pics" and "i just got the new iphone 4 and theres a discount! click here!". its getting very annoying. is it something that I did to get them to message me? or is it something my friends did to get them to get hacked by the robot? please help.