this term came from Rita Hayworth, the gorgeous, notorious movie star whose image was painted on the side of the first atomic bomb exploding at the Bikini Atoll in World War 2. (so she was a literal BOMBSHELL! :) This started the trend of calling stunning, sexy females bombshells- and the phrase is STILL commonly used today.
A screenshot you found online or in the Google dot com search results featuring incredibly ordinary information. Announced with much fanfare like a Wikileaks data dump, but is really just a quote from someone's tweets. Generally posted on Twitter dot com, always including a tag to alert the FBI.
Another Antifa bombshell is coming tomorrow. Here is the same photo once again, and 100% verified evidence that Antifa did the moon landing.