F*****g viruses or whatever

So am I the only unlucky one to get my website messed up with spam and stuff ?
How does this even happen ??!!
I was checking out a website, clicked a link in the blogroll, ended up on adult friend finders of whatever. So then I went to the previous page, reclicked the link and go to the website I was looking for. And there, I get this firefox page informing me the site is an “attack site” :huh:.
Yeah, ok the site was carlos ulloa from pv3d’s website. Wierd.
Then I decide to fix something on my blog and WOW, php parse errors all over the place, and hidden iframes and stuff in my source code… WHAT THE HELL!:m:

Anyone had this before, or knows what it is or how it gets into my php files and injects pieces of html ?