Adversaries may develop malware and malware components that can be used during targeting. Building malicious software can include the development of payloads, droppers, post-compromise tools, backdoors (including backdoored images), packers, C2 protocols, and the creation of infected removable media. Adversaries may develop malware to support their operations, creating a means for maintaining control of remote machines, evading defenses, and executing post-compromise behaviors.(Citation: Mandiant APT1)(Citation: Kaspersky Sofacy)(Citation: ActiveMalwareEnergy)(Citation: FBI Flash FIN7 USB)

As with legitimate development efforts, different skill sets may be required for developing malware. The skills needed may be located in-house, or may need to be contracted out. Use of a contractor may be considered an extension of that adversary's malware development capabilities, provided the adversary plays a role in shaping requirements and maintains a degree of exclusivity to the malware.

Some aspects of malware development, such as C2 protocol development, may require adversaries to obtain additional infrastructure. For example, malware developed that will communicate with Twitter for C2, may require use of [Web Services](https://attack.mitre.org/techniques/T1583/006).(Citation: FireEye APT29)
Malware
source_name: mitre-attack  url: https://attack.mitre.org/techniques/T1587/001  external_id: T1587.001     source_name: Mandiant APT1  description: Mandiant. (n.d.). APT1 Exposing One of China’s Cyber Espionage Units. Retrieved July 18, 2016.  url: https://www.fireeye.com/content/dam/fireeye-www/services/pdfs/mandiant-apt1-report.pdf     source_name: Kaspersky Sofacy  description: Kaspersky Lab's Global Research and Analysis Team. (2015, December 4). Sofacy APT hits high profile targets with updated toolset. Retrieved December 10, 2015.  url: https://securelist.com/sofacy-apt-hits-high-profile-targets-with-updated-toolset/72924/     source_name: ActiveMalwareEnergy  description: Dan Goodin. (2014, June 30). Active malware operation let attackers sabotage US energy industry. Retrieved March 9, 2017.  url: https://arstechnica.com/information-technology/2014/06/active-malware-operation-let-attackers-sabotage-us-energy-industry/     source_name: FBI Flash FIN7 USB  description: The Record. (2022, January 7). FBI: FIN7 hackers target US companies with BadUSB devices to install ransomware. Retrieved January 14, 2022.  url: https://therecord.media/fbi-fin7-hackers-target-us-companies-with-badusb-devices-to-install-ransomware/     source_name: FireEye APT29  description: FireEye Labs. (2015, July). HAMMERTOSS: Stealthy Tactics Define a Russian Cyber Threat Group. Retrieved September 17, 2015.  url: https://www2.fireeye.com/rs/848-DID-242/images/rpt-apt29-hammertoss.pdf     