Amber Langford and Annie Collinge, two 19-year-old students from Chester University, dressed up as the 9/11 twin towers for Halloween.
They entered a costume competition at Chester nightclub Rosies.
And they came first, taking home £150.
Twitter users were outraged, and many tweeted the nightclub to express their anger.
Pretty soon @RosiesProblems, a Twitter account for "people that go to Rosies to have a laugh and joke about their night out the next day" started getting abuse too.
So they cleared things up with an explanatory tweet.
As the story made headlines around the world, both girls deactivated their Twitter accounts.
Which is just as well, because the abuse started to get very personal.
I didn't know anything about it, but I'm not happy at all. She knows I'm a pilot and that's not cool at all. We will be having a little chat, I think.
We are extremely concerned that an award of vouchers was made to two young women who were dressed in a distasteful and offensive manner.There was a serious error of judgement made on the evening by a contracted DJ to award such a prize and we apologise to anybody who may have been upset or offended by this.A full investigation by the company is taking place.
We utterly condemn the appalling photos.Both organisations have begun an urgent investigation with a view to taking the necessary action.
We never meant to be offensive, but we apologise if any offence was caused.The idea was to depict a modern-day horror that happened in our lifetime and was not intended as a joke.