Sounds to me more like you have a spyware problem or virus on your computer.
Hey I have kaspersky and I just got the same Pop Up. Weird..
AVG website scanner isn't finding any problem either:http://www.avg.com.au/resources/web-page-scanner/
Wow! I think I'm getting myself Kapersky...
Apparently this virus injected itself into a some 300,000 wordpress sites! You may want to download a free trial of kaspersky to keep yourself safe!
What does it do specifically? (the virus)
Nothing. It might redirect you to come pharmaceutical site but that's it.
Is this the virus you are referring to? This one sometimes redirects to payload sites, which download nasty viruses like this one.