On Wednesday, The Huffington Post and our Australian partner Fairfax Media published the results of a months-long investigation into Unaoil , a mysterious Monaco-based firm registered in the British Virgin Islands.

Unaoil and its subcontractors bribed foreign officials to help major multinational corporations win contracts, tens of thousands of the company's internal documents show. The investigation illustrates just how complicit big Western companies are in corruption overseas. It also shows that by enabling corruption, these companies fuel the kind of political instability that allows insurgencies like the self-described Islamic State to grow.

It's a complicated story, so we're explaining it all for you here.

What is Unaoil?

Unaoil says that it provides international clients with "industrial solutions to the energy sector in the Middle East, Central Asia and Africa." Its business is "very basic," founder Ata Ahsani said. "What we do is integrate western technology with local capability." But the emails suggest that Unaoil's business plan was far more complicated.

Who's in charge?

Unaoil is controlled by the wealthy Ahsani family of Monaco . Its patriarch, Ata Ahsani, was in the engineering business in Iran before the 1979 revolution. Like many secular and relatively wealthy Iranians, he left to establish a life in the West. By 1991, he had set up Unaoil. Today, he is its chairman. The CEO is his son Cyrus, a noted Monaco socialite who serves as treasurer of the small nation-state's Ambassadors Club, whose honorary president is Prince Albert II. Saman Ahsani, Cyrus' brother, is Unaoil's COO and a prominent figure in London's Iranian expatriate community.

Which companies worked with Unaoil?

American companies Halliburton, Honeywell, KBR and FMC Technologies; Korean manufacturers Samsung and Hyundai; U.K.-based Rolls-Royce; and Germany-based Man Turbo all worked with Unaoil, according to internal documents. So did hundreds of other firms, according to an internal Unaoil spreadsheet.

What is HuffPost basing its stories on?

HuffPost and Fairfax Media obtained tens of thousands of internal Unaoil documents, most of which are dated between 2003 and 2012. Fairfax writes that the source or sources who provided the documents never asked for money.

What they wanted was for some of the wealthiest and most powerful figures in government and companies across the globe to be exposed for acting corruptly, and with impunity, for years, Fairfax Media explains. Want to know more about how this investigation came to be? Reporter Nick McKenzie has the story .

Why does this matter?

This type of corruption leads to political instability, undermines trust in already distrusted governments, makes business unpredictable, and helps terrorists .

What are the potential legal consequences for Unaoil and its clients?

Many of the companies that contracted with Unaoil have close ties to industrialized nations who are members of the Organization for Economic Cooperation and Development, or OECD. Since all OECD member countries are committed to international standards barring the bribery of public officials in business transactions, any of those governments could, in theory, investigate companies in their jurisdiction that worked with Unaoil at the time it was engaging in global corruption.

Compliance with the OECD standard looks different in each country, depending on the laws and enforcement mechanisms there. In the U.S., a federal law called the Foreign Corrupt Practices Act, or FCPA, prohibits businesses from working with companies or individuals that they know -- or should know -- bribe foreign officials. U.S. prosecutors can and do apply this law to non-U.S. firms , especially ones that do business in the U.S or issue stocks on U.S. exchanges. Eight of the ten largest FCPA settlements in history -- all of them over $100 million -- were with firms based outside of the U.S. (One of the largest was with KBR, which is implicated in this scandal, too .)

What if the companies didn't know Unaoil was paying bribes?

It won't protect them from penalties. The FCPA doesn't just criminalize foreign bribery: It makes it a crime to be "deliberately ignorant" or "willfully blind" to corrupt practices. Simply failing to keep proper records, or properly investigate whether a partner company was doing business above-board, can trigger liability under the FCPA.

But at least some of the companies probably did know about the bribes. In one particularly egregious email, Kelsey Kalinski, the president of a Canadian fracking firm called Canuck Completions, emailed his colleagues and a Unaoil employee, Foroohar Farzadnia, to ask about a deal in Libya. "What we are curious about is to what type of Baksheesh [a common slang term for bribery] is needed to present to these men in order to get work started," Kalinski wrote. "I believe this is common practice in Libya, but we are not sure how to handle this. Is this something that needs to be done after work hours one on one? A added value amount to the ticket for them, or a flat fee a month, we are not sure. What are your thoughts on this?" (The email was forwarded to Unaoils top executives, one of whom said he didnt know what Kalinski was talking about.)

What if the bribes were discussed but never actually paid?

It doesn't matter. The FCPA criminalizes the act of agreeing to or promising to bribe a foreign official. "The statute does not require a completion of a bribe," says Andy Spalding, an FCPA expert at the University of Richmond's law school. "It can be an offer or a promise to pay. Those alone give rise to liability. It doesn't matter if the bribe was consummated."

Where did Unaoil operate?

Unaoil operated in Iraq, Kazakhstan, Libya, Syria, Tunisia and more than a dozen other countries. Here's a map:

Most of the countries where it operated are considered highly corrupt, according to Transparency International's Corruption Perceptions Index .

What was Unaoil doing in Iraq?

Unaoil made payments in an attempt to influence at least five Iraqi officials, four of whom it described in the emails using codenames:

• Hussain al-Shahristani, a former head of the oil ministry and deputy prime minister. The company gave him the codename Teacher. He now runs Iraq's education ministry.

• Kareem Luaibi, who succeeded Shahristani as oil minister, and was referred to as M.

• Kifah Numan, head of the South Oil Company until 2009.

• Dhia Jaffar al-Mousawi, director general of Iraqs South Oil Company from 2009 until 2015, when he became the countrys deputy oil minister . Emails refer to him as Lighthouse.

• Oday al-Quraishi, another official at the South Oil Company, codenamed "Ivan."

The two most important people Unaoil tried to bribe in Iraq were so high up that the company was compelled to use a fixer -- Ahmed al-Jibouri, codenamed "Doctor" -- to try to reach them. In 2010 and 2011, Unaoil paid Jibouri at least $20 million in an attempt to influence Shahristani and Luaibi.

Unaoil employee Basil Al Jarah, who handled the company's Iraq business, implied he believed Jibouri was more than a lobbyist, and was instead passing part of his payment on to Shahristani and Luaibi. "He is a tool," Al Jarah wrote in a Skype conversation that was copied and pasted into an email. "The people above him are right assholes and greedy." In another email, Al Jarah described the promise of a "1.5 days holiday" -- code for a $1.5 million payment -- for Jibouri's "side." Jibouri "transferred that info to teacher and on that basis teacher gave it the OK," Al Jarah added.

How did you figure out what the codewords and codenames meant?

Unaoil employees were careful, but not careful enough. The full context of the emails made clear that "holidays" were bribes, with one day corresponding to $1 million. Sometimes, an invoice for the corresponding dollar amount would be attached directly to an email mentioning a "holiday."

In several emails, Unaoil employees included enough details to identify the people behind the codenames. In one of the emails, for example, Unaoil employees describe the prime minister sending "Teacher" to inspect a particular site. News reports from that day -- and later replies in the email chain -- make clear that "Teacher" is Shahristani.

Shahristani denies that he was ever involved in corrupt activity and says he has no knowledge of Al Jarah.

Shahristani is a really big deal, right?

Yes. He is currently Iraqs minister of higher education. He served as minister of energy from 2006 to 2010, as deputy prime minister under Nouri al-Maliki from 2010-2014, and briefly as minister of foreign affairs in 2014.

When Saddam Hussein was still in power, Shahristani, a nuclear physicist by training, was imprisoned for years in Abu Ghraib after refusing to assist with his countrys nuclear weapons program. Because of this, Shahristani can rally popular support by presenting himself as one of Iraq's cleanest politicians.

There's no direct evidence that the money Unaoil paid to Jibouri actually got to Shahristani or Luaibi. But that doesn't get the company off the hook, since even agreeing to pay a bribe, regardless of whether the bribe was completed, is illegal in many countries.

What was Unaoil doing in Kazakhstan?

U.S. construction giant KBR hired Unaoil to help it secure a joint contract with Petrofac , a British company, in Kazakhstans Kashagan oil field starting in 2004.

Internal emails between KBR (which was a subsidiary of Halliburton until 2007) and Unaoil employees show that KBR had tried, unsuccessfully, to win projects in the oil field since 1998. In a February 2005 email, a man named Richard Stuckey with a Halliburton email address wrote to Unaoils Peter Willimont, telling him to start hobknobbing [sic] with insiders immediately. My feeling is that a good spaghetti house is where it is at of course a little shashlik for lunch is good to digest also, Stuckey wrote. Spaghetti and shashlik were codenames for an Italian oil company operating in the Kashagan and Kazakh government officials.

Unaoil delivered. It put Leonida Bortolazzo, a consultant to a wing of Kazakhstans state-owned oil company and a former manager at the Italian oil firm Eni, on its payroll. In exchange for Bortolazzo leaking documents and directing work toward Unaoils client, Unaoil paid Bortolazzo as much as $80,000 a month.

At the same time, Unaoil worked to gain favor with Kazakh government officials. In 2008, the group spent thousands of euros on lavish hotel rooms for top oil executive Kairat Boranbayev and his aides when they visited Monaco.

Whoa, that's pretty bad for KBR.

Yes -- and it gets worse. In 2009, the Houston-based company plead guilty to bribing Nigerian officials in exchange for lucrative contracts from 1994 to 2004. (Halliburton, then its parent company, reached a civil settlement with the SEC in 2009 as well.) As part of that plea bargain, KBR agreed to waive many of its rights if it broke bribery laws again. The Justice Department may decide that Unaoil's work for KBR in Kazakhstan, much of which took place after the investigation into the Nigerian bribes began, could trigger a breach in this plea agreement.

After coming under investigation, KBR made some internal changes to its anti-corruption enforcement mechanisms -- but these changes did not stop the group from working with Unaoil. In 2007, KBR hired Kevin Abikoff from Hughes Hubbard and Reed, a Washington-based law firm, to conduct a due diligence investigation into KBR's past work with Unaoil. Abikoff wrote a 51-page report of his findings and concluded that working with Unaoil did not pose a risk of violating corruption laws.

Wait, how did Unaoil move all of this shady money around?

Banks are supposed to take steps to ensure that they aren't pumping criminal cash through the financial system. HSBC and Citibank served as Unaoil's private bankers , processing transactions and managing a slate of accounts that helped Unaoil and the Ahsani family shield information about its activities from outsiders. The Ahsanis had a particularly cozy relationship with their banker at Citi, who secured them tickets to an elite car show in Monaco and helped them get into key events with public officials. Whether the banks violated U.S. anti-money laundering law depends on whether authorities determine that Unaoil's bribes were in fact illegal, and whether American regulators determine that the banks should have done more to ensure they weren't helping criminals. Both Citibank and HSBC have run afoul of anti-corruption and money laundering laws in recent years.

What was Unaoil doing in all those other countries where it worked?

We'll have more on that soon. Check back for updates.

Who's in charge of investigating whether crimes were committed here?

Because Unaoil worked for corporations from a range of different countries -- such as KBR in the U.S., Rolls-Royce in the U.K. and Leighton Holdings in Australia -- it could be vulnerable to investigations by several different law enforcement agencies.

The U.S. Department of Justice and the Securities and Exchange Commission charged KBR with bribery in 2009, and could open a probe into the groups work with Unaoil in Kazakhstan. U.S. regulators can also target any number of the involved international companies if they are listed on a U.S. stock exchange, operate a U.S. office or use U.S. banks. Even simply using U.S. dollars to pay bribes can trigger liability.

Australian regulators are expected to pay close attention to the evidence of Unaoil's work for Australian contractor Leighton Holdings . Leighton has been under federal investigation for five years and even changed its name to CIMIC Group last year to move on from allegations of paying bribes in Iraq between 2009 and 2011.

But British investigators could take the most aggressive approach of all.

Wait, why does the U.K. care so much about this?

The U.K. Serious Fraud Office is likely to act even more broadly. In 2010, British legislators crafted a tough new anti-bribery law that criminalizes even more activities than the American FCPA. The British law makes it a crime to bribe anyone, not just foreign officials, according to the Association of Corporate Counsel . It also does not require prosecutors to prove corrupt intent, does not accept the excuse of bribes being "local custom" and holds liable those who accept bribes. The U.K. made its law tighter in this way because its previous anti-corruption regulation set too high a bar for successful prosecution, the legal association suggests -- which means that Unaoil and similar companies with British ties should be even more scared than they had to be before the law came into effect in 2011.

But the new bribery act is not retroactive . Any of Unaoils corrupt activities prior to 2011 would be prosecuted under the old, weaker law. Britain is apparently already investigating Rolls-Royce, which severed ties with Unaoil in 2013. The company told HuffPost it is cooperating with authorities and cannot comment on ongoing investigations.

Where can I read more?

Check out our other stories on this:

• Theres A Huge New Corporate Corruption Scandal. Heres Why Everyone Should Care.

• U.S. Oil Industry Giant Paid Millions To A Company At The Center Of Huge Corruption Scandal

• How I Exposed A Corporate Bribery Scandal Involving The Biggest Names In The Oil Business

• Inside The Battle Against Global Corruption

• Top Washington Lawyer Cleared Unaoil In Anti-Corruption Report

• Big Banks Aided Firm At Center Of International Bribery Scandal

You can read our Australian colleagues' full investigation here . You should definitely read their piece on Unaoil's dealings in Iraq .

You can also follow us on Twitter: @AkbarSAhmed , @NickBaumann , @PaulBlu , @JessicaSchulb , and, of course, @HuffingtonPost .