Problem with "virus"

Hi,

I noticed today that several of my posts have now a link to an online pharmacy… This was added to most of my posts, in different places, one time on each post…

I’m guessing this is some kind of a virus…

Anyone knows how I can remove this? If I edit each post I can do it, but I was thinking if there was a better way to remove all of them and most important, to prevent this from happening again…

Thanks