What are caffeinated alcoholic beverages (cabs)? are they harmful?

Very harmful: They are a combined product with both ingredients. Or popular to combine on own. Some studies indicate increase consumption of alcohol. Caffiene may block cues to being intoxicated. One study showed persons who mix alcohol with energy drinks had twice as many drinking days per month and twice as many days of drunkenness. Combo reversed some effects of intoxication, but not actual error rates.

Yes they are: Many beverage companies have added caffeine to not only energy drinks (5 hour energy, red bull) but to alcoholic beverages, chiefly beers and malt liquor, and ales. This is a trick to get you to feel less sleepy when you drink, so that you may drink more. It does not reduce the ill effects of alcohol on your performance, driving etc., but masks the effects of the alcohol. They may yet be banned.