(NewsNation) — Classified documents about the war in Ukraine were leaked online last week. Information in the documents could be damaging to Ukraine as well as to U.S. intelligence. Here’s what we know and don’t know about the documents.

What was leaked?

Classified Pentagon documents were published on social media sites, including Twitter, last week. The leaked documents appear to be briefing papers that would be used to inform U.S. officials, and the leak includes photos of the papers.

Are the documents real?

At this point, U.S. officials said the documents appear to be legitimate, though there is an investigation into the leaks. There has also been speculation that some of the documents may have been altered before being posted.

“These photos appear to show documents similar in format to those used to provide daily updates to our senior leaders on Ukraine and Russia related operations, as well as other intelligence updates,” a senior Pentagon official told reporters.

Where did the leak come from?

The Pentagon and Justice Department are investigating the source of the leak. Deputy Pentagon Press Secretary Sabrina Singh told NewsNation: “We are aware of the reports of social media posts, and the department is reviewing the matter.”

The Pentagon refused to say how many people might have access to such documents and a spokesperson for the National Security Council admitted they don’t know if more leaks might be coming.

What was in the documents?

Information on the war in Ukraine was included in the leaked documents, which also indicated the U.S. is spying on Ukrainian President Volodymyr Zelenskyy as well as Russian President Vladimir Putin. Intelligence analysis included in the documents also suggests the U.S. has been spying on allies including South Korea and Israel. National security information on the Middle East and China was also leaked.

One potentially damaging piece of information included in the documents was information on which Kremlin agencies U.S. intelligence had been able to infiltrate.

Why are the documents still online?

The documents have been recirculated on many social media sites, making it difficult to track down where they might be shared. Social media companies could attempt to remove documents from their platforms, but Twitter, at least, doesn’t seem to be planning to.

“Yeah, you can totally delete things from the Internet – that works perfectly and doesn’t draw attention to whatever you were trying to hide at all,” tweeted Twitter owner Elon Musk.

What makes this different from other leaks?

The biggest thing that makes this leak bigger than others, like the Pentagon Papers or Wikileaks, is how recent the documents are. They could be especially damaging because they contain information that could allow foreign intelligence agencies to get a better picture of how the U.S. conducts its own intelligence operations.

Will the leaked documents change the situation in Ukraine?

There are already reports that Kyiv is being forced to change strategies in response to the leak, which included dire predictions about Ukraine’s ability to continue air defense. Russia is undoubtedly paying close attention as well and Business Insider reported Putin may be considering bringing out fighter jets that have been held in reserve based on that information.