The Democratic National Committee alerted the FBI on Tuesday that it had detected an advanced effort to hack into its voter database, according to a new report.

A cloud service provider and security research firm contacted the DNC early Tuesday that a fake login page had been created to try to collect usernames and passwords that would give access to the party’s database, a source told CNN.

The page appeared to look like the access page Democratic Party officials and campaigns use to log into Votebuilder, which hosts the voter database, the CNN report said.

It is not clear who may have been behind the attempted hack. The DNC does not believe its voter files were accessed or changed.

The report comes a day after Microsoft said it had detected and shut down websites created in recent weeks by hackers linked to a Russian military intelligence unit that sought to influence the 2016 election. The websites targeted conservative think tanks who have been critical of Russia. Microsoft also detected websites imitating Senate websites.

An indictment earlier this year from special counsel Robert Mueller alleges 12 Russian intelligence officials stole thousands of emails from the DNC and Hillary Clinton’s campaign chairman John Podesta, and transferred them to WikiLeaks during the presidential campaign.