I didn't mean to alarm anyone, but this has been in the news lately, so it's the first thing I thought of, but if it's not happening on any other sites, you may be okay. Craig's list may be redirecting you just because of location. This has "Los Angeles" in the address.
Here's what the actual address says:
http://losangeles.craigslist.org/lgb/pet/3345890042.html
I'm now browsing "InPrivate" and I have security set up very high because the Google double click ads were slowing me down, maybe that's why it took me to the actual site because they couldn’t figure out my location.
Here' more about the redirect virus.
Google Redirect Virus Removal | How To Remove Search Redirect Virus Easily There are more than one redirect virus though, this is just one of many.