UPDATE 4: (3:56 p.m., Dec. 22): Justine Sacco has written a public apology, noting, "Words cannot express how sorry I am, and how necessary it is for me to apologize to the people of South Africa, who I have offended due to a needless and careless tweet."

UPDATE 3 (5:35 p.m., Dec. 21): IAC says it has fired Justine Sacco.

UPDATE 2 (12:24 a.m., Dec. 21): Justine Sacco's Twitter account appears to have been deleted. Meanwhile, her tweet had become a trending topic of global discussion, with brands and Web celebrities alike joining in the fray.

UPDATE: A rep for IAC tells Valleywag: "This is an outrageous, offensive comment that does not reflect the views and values of IAC. Unfortunately, the employee in question is unreachable on an international flight, but this is a very serious matter and we are taking appropriate action."

Original item below:

If Justine Sacco is on a flight to Africa right now, I don't envy her the notifications that will be waiting for her when she lands.

Sacco, senior director of corporate communications at the massive digital holding company IAC, apparently tweeted the following earlier today: "Going to Africa. Hope I don't get AIDS. Just kidding. I'm white!"

The tweet has since attracted scorn and disbelief from Silicon Valley and far beyond. IAC is no small player in the digital realm. The company owns many popular websites, including About.com, Match.com, Vimeo, CollegeHumor, OkCupid and Urbanspoon.

Of course, this is the Internet, where things aren't always what they seem. The @JustineSacco Twitter account appears to be legitimate, though anyone could theoretically have gotten ahold of her phone and posted the message.

That said, many have been digging through her earlier tweets and pointing out messages like this one from January of this year:

I can't be fired for things I say while intoxicated right? — Justine Sacco (@JustineSacco) January 30, 2013

We've reached out to Sacco for comment and will update this item if we hear back.