In a Reddit post, the substance of which was deleted before I thought to take a screenshot, an international test-taker in Saudi Arabia reported that the international SAT given today was posted to multiple WhatsApp groups at 1AM (presumably local time). As a result, according to this person, most people at the testing center came with the answers memorized. Other posts establish that this was the same test given as the October school-day test in the US. [Edit: And here's what appears to be a student in Egypt reporting the same thing.]
If these reports are accurate, this is obviously a serious security breach, and the timing strongly hints at an insider corruption. If the WhatsApp leak went out at 1AM AST (= UTC+3), that is 7AM in Seoul, 9AM in Sydney, and 11AM in Auckland. That means that the test was leaked before students in New Zealand were even dismissed.
I can see two possibilities for how it occurred. If the leak occurred from New Zealand, it's possible that a student taking the test recognized the content and texted that fact to an associate during a break, and that associate then distributed the test itself. This, of course, requires that the student in the exam room had previously studied the October school-day test, which had not been released, so that itself is another security breach. The other possibility, and given the timing the one that seems more likely, is that someone entrusted with administering the test sent out the information, either identifying the similarity with a test that they already had from its previous use in the US, or simply scanning a copy once they opened up the test packets Saturday morning.
No matter how it happened, this incident is yet another illustration that well-organized test pirates have thoroughly compromised the current test-security measures that the College Board is using, and until they make a radical change, such as delivering all international tests via computer, these events are going to continue with great regularity.