Story highlights Media reports say the NSA tapped the phones of about 35 world leaders

Key questions have emerged about what Obama knew, and his response

Leaders in Europe and Latin America demand answers, say they're outraged

It may not be as gripping as a spy novel, but things are heating up after the latest reports of espionage by the U.S. National Security Agency.

International leaders say they're outraged and the Obama administration says it's investigating.

Here are five key questions to keep in mind:

1. Are President Barack Obama's hands clean in this?

It's not really clear.

The Wall Street Journal reported an internal review of U.S. surveillance programs that started this summer revealed the NSA had tapped the phones of about 35 world leaders and that the White House ordered a halt to some of it

That would suggest the President did not know about the programs for the nearly five years he has been in office.

Senate Intelligence Committee Chairman Dianne Feinstein says neither Obama nor her panel knew the United States was collecting communications of allied leaders, like German Chancellor Angela Merkel.

A senior administration official separately confirms to CNN some details of the Journal report, saying the White House did not know about the program until an until an internal review over the summer, after which some of it was stopped.

Targeting of German Chancellor Angela Merkel's phone, however, did not end until quite recently, the senior official said.

2. Was Obama kept in the dark?

Another U.S. official says, however, that Obama was briefed and given detailed documents describing what's known as the framework for the surveillance programs.

One targets leaders in specific countries, which he would have been briefed about. It's not known if the description mentioned Merkel, but countries targeted would have been included.

It's not reasonable to expect that the President would have been involved in or necessarily briefed on decisions about individual intelligence targets, argued another senior administration official.

Rather, the president approves a set of intelligence priorities and then it's the responsibility of his administration to determine how to carry those out.

The explanation was backed by a former senior administration official who worked on national security for the Obama White House.

"I really doubt he had to sign off on something like that or get into the details," the former official said.

3. What has Obama done about it?

That's a key question.

In a USA Today op-ed published last week, Obama's homeland security and counterterrorism adviser Lisa Monaco conceded that recent "disclosures have created significant challenges in our relationships."

To address them, the President has ordered a "review (of) our surveillance capabilities, including with our foreign partners," she wrote.

A report on that effort is due by the end of the year.

As accusations mount and the issue becomes increasingly thorny diplomatically, it's unclear what Obama has said and done behind closed doors.

4. Who's upset about this?

In the United States, some have dismissed the foreign leaders' criticism as political bluster, arguing that spying is a common practice in international relations , even for allies.

5. What would the United States hope to learn?

The United States says its surveillance programs are for the purpose of foiling terrorist plots, but there are many political reasons for interest in communications of world leaders.

For example, some media reports suggest the tapping of Merkel's phone increased in 2010, around the time of the financial crisis in the Eurozone, in which Merkel was a major player.

The U.S also wants as much information as possible about the actions of other states to make its own decisions about important foreign policy issues, such as Syria and Iran. At the end of the day, allies cannot automatically count on each other's loyalty.

"We do have a fantastic intelligence capability, worldwide against all kinds of potential issues and concerns. We are vulnerable, as was shown on 9/11, and you never know what you're going to need when you need it," said Cheney.