At first, I thought this was a joke but it seems there really is a comet called ISON that is heading towards earth. It has already affected Mars and will reach earth in 2028. It won't hit us but it will cause major damage.
I for one welcome the apocalypse - I'm pretty bored and I would welcome the change.
Seriously, I doubt this comet will do much. I know what comets are, especially (mostly) vapors and gasses coming from a tiny nucleus of hard matter. That nucleus would have to hit the earth to do serious damage. The tail won't do much - at worst take out a few satellites, at best a lovely light show.
A lot of comets come here to earth, and a lot of them do tend get really close to earth, that's why we see some of them really clearly. Doesn't mean that it will hit the earth though. Although it could, but if it does, NASA or other space agency around the world would tell it since it will be a matter of planet-wide security.
The last I heard when it came to incoming objects that can't be deflected, silence is what we would hear from Government types in the USA and assume other nations.
I forget where I read the paper/proposal (it was a Nasa/JPL paper not some loon screaming out their arse) that the best way to deal with the problem is allow it to hit then concentrate on clean up.
Why? because the panic of an informed public would do far much more damage before the impact event than the event itself would do.
EXAMPLE: The economy was far more likely to collapse in the days before an impact just from the panic, the economy stands a far greater chance of not collapsing even if a major city like New York was directly impacted.
It was very logical and made a lot of sense. Terrifying sense and revealed much about sociologists and psychologists and exactly how they view the general public.