Downloads of Folx and Elmedia player were infected with Proton, a Remote Access Trojan, after Eltima's servers were hacked. The Proton backdoor lets attackers access browser information, keylogs, usernames, passwords, macOS keychain data, and more.
Apple and Eltima have disabled the developer ID that was used to sign the Proton-infected software bundle, and Eltima is working with Apple to figure out what happened.
Anyone who was impacted by the malware will need to reinstall macOS to get rid of it. Eltima says it has taken action to prevent against further attacks and improve its server security. Clean versions of Elmedia Player and Folx are now available from the Eltima website.