(Dado Ruvic/Illustration/Reuters)

In this occasional series, we will bring you up to speed on the biggest national security stories of the week.

This week, Facebook announced that a Russian company had spent $100,000 on thousands of political advertisements during the presidential election campaign. It is unclear whether the firm, described as a “troll farm” based in St. Petersburg with a history of peddling pro-government messages, had any connections with the Trump campaign.

Alex Stamos, Facebook's chief security officer, wrote in a blog post that the sale of the ads goes as far back as 2015. The company said the ads sough to amplify “divisive and political messages,” such as gun rights and LGBT matters. However, some of the ads specifically referenced Republican nominee Donald Trump and Democrat Hillary Clinton, according to people who spoke to The Washington Post.

Here's what you need to know:

What did Facebook discover? 

Facebook began to look into political ad-buying in the spring, according to people familiar with the matter. Now, its findings reveal that potentially 3,300 of the company's advertisements were connected with the Russian firm named Internet Research Agency, according to a Facebook official.

As many as 470 fake Facebook accounts and pages were created to peddle messages around issues related to the election, a tactic Russian trolls liberally employ to sow discontent.

Facebook declined to share any of the ads, saying that “our data policy and federal law limit our ability to share user data and content.” However, it did turn over copies of the ads as well as the identities of the buyers to special counsel Robert S. Mueller III on Wednesday, according to Reuters.

Mueller, along with a team of 16 other investigators, is overseeing an investigation into Russian collusion with the Trump campaign.

What do we know so far in Russia's efforts to influence the election?

U.S. intelligence officials have concluded that Russian President Vladimir Putin was personally responsible for a disinformation campaign to help Trump clinch the White House.

Ben Rhodes, former deputy national security adviser under President Barack Obama, summarized that the Kremlin's cyber efforts went beyond just hacking.

“The Russians were playing this much bigger game, which included elements like released hacked materials, political propaganda and propagating fake news, which they’d pursued in other countries,” Rhodes said.

Putin has repeatedly denied and joked about the allegations, calling them “useless and harmful chatter.” Putin has also suggested that “patriotic” Russian hackers may have been acting independently of the Russian government. That runs counter to a declassified report released in the beginning of the year that shows the Kremlin's role to damage Clinton's chances of winning was significant and was conducted on an unprecedented scale.

How was the Russian company able to buy the ads?

Federal laws bars foreign citizens and governments from spending money to influence elections in the United States. The Federal Election Commission explicitly states that foreign nationals, governments, political parties and corporations are not allowed to contribute funds to help any candidates in local or national elections.

However, political ads that advocate for an issue rather than a specific individual running for office fall into a legal gray area and Facebook may not have explicitly broken any laws in this instance.

What has Facebook done to stop the spread of misinformation? 

Last year, Facebook chief executive Mark Zuckerberg wrote a post saying “more than 99%” of what people see on the social network is authentic and that the company was already working toward preventing the spread of fake news and hoaxes. Zuckerberg, along with Google, vowed to also crack down on ads that fund the phony stories. So far the company has followed through. Just last month, it announced Facebook pages will no longer be able to advertise if their shared news articles were repeatedly marked as false.

The company also purged about 30,000 fake accounts in the run up to the French election in May and “tens of thousands” more before the British election.

The campaign of eventual president Emmanuel Macron was hit with a massive cyberattack shortly before the vote. Even though U.S. intelligence agencies as well as cybersecurity firms tied the actions to the same Russian hackers who infiltrated Clinton's campaign, French officials have denied it.

U.S. officials told Reuters in July that about two dozen Facebook accounts were created by Russian intelligence agencies attempted to spy on Macron's campaign. Russia has denied interfering the French election.