I was also on chrome, chrome isn't immune. But a browser cache clear should fix any browser that it's repeating on.

I would say either the ad provider has a dodgy ad in their list they need to remove or there's a virus on the P-WRX server (I've seen this before, but it would hit you more consistently, I don't think this is it) or thirdly and most likely I suspect possibly a third party is injecting and replacing the ads, some ISP's do it but any upstream DNS server can do it.

It could also be none of the above, I don't really have enough information to go on. It was the top banner if that helps. It is weird though. Still has anyone noticed it lately? Maybe it's already been stopped.