Merged a thread with the existing one on this issue to avoid messaging duplication.
We're working to determine which ad is causing this messaging to occur. This kind of advertising is *not* approved by FT, and will immediately be blocked when it is located. Meanwhile, be assured that despite the message it shows you, you do not have a virus (from this) and FT is not infected. This is an advertisement that appears to be exploiting a hole in Internet Explorer to show a false virus alert.
One way to avoid it is to switch browsers to Chrome or Firefox.
I'll update as soon as I have new information; thank you for hanging in there with us while we resolve this.
Paul