The backdoor - dubbed Vernot - can perform all the usual things malware of this kind does: it harvests system information and sends it to a remote server (or even possibly to the same Evernote account it picks its commands from), and can download, execute, and rename files.
Whether the information is dropped off at the account couldn't be verified, as the login credentials embedded in the malware were no longer valid - likely because of the service-wide password reset executed by Evernote following the recent breach.
"As stealth is the name of the game, misusing legitimate services like Evernote is the perfect way to hide the bad guysí tracks and prevent efforts done by the security researchers. Because BKDR_VERNOT.A generates a legitimate network traffic, most antimalware products may not readily detect this behavior as malicious," the researchers pointed out. "This can be troubling news not only for ordinary Internet users, but also for organizations with employees using software like Evernote."
This is not the first time that a popular online service is used as a way for malware to communicate with its C&C servers - Google Docs, Sendspace, Twitter and others have been misused in the past.