HAMMERTOSS is a backdoor that was used by APT29 in 2015.  
|Enterprise||T1071||.001||Application Layer Protocol: Web Protocols||
The "Uploader" variant of HAMMERTOSS visits a hard-coded server over HTTP/S to download the images HAMMERTOSS uses to receive commands.
|Enterprise||T1059||.001||Command and Scripting Interpreter: PowerShell||
HAMMERTOSS is known to use PowerShell.
|Enterprise||T1001||.002||Data Obfuscation: Steganography||
HAMMERTOSS is controlled via commands that are appended to image files.
|Enterprise||T1573||.001||Encrypted Channel: Symmetric Cryptography||
Before being appended to image files, HAMMERTOSS commands are encrypted with a key composed of both a hard-coded value and a string contained on that day's tweet. To decrypt the commands, an investigator would need access to the intended malware sample, the day's tweet, and the image file containing the command.
|Enterprise||T1567||.002||Exfiltration Over Web Service: Exfiltration to Cloud Storage||
HAMMERTOSS exfiltrates data by uploading it to accounts created by the actors on Web cloud storage providers for the adversaries to retrieve later.
|Enterprise||T1564||.003||Hide Artifacts: Hidden Window||
HAMMERTOSS has used
|Enterprise||T1102||.003||Web Service: One-Way Communication||
The "tDiscoverer" variant of HAMMERTOSS establishes a C2 channel by downloading resources from Web services like Twitter and GitHub. HAMMERTOSS binaries contain an algorithm that generates a different Twitter handle for the malware to check for instructions every day.