Underground markets offer a great variety of services for cyber criminals to profit from. These forums offer items ranging from physical world items like drugs and weapons to digital world items such as spam/phishing delivery, exploit kit services, "Crypters", "Binders", custom malware development, zero-day exploits, and bulletproof hosting.
The underground is filled with a heavy amount of jargon and slang that may be unfamiliar. Crypters are tools that encrypts malware in order to bypass detection by Antivirus engines. Binders are tools used to trojanize a legitimate program with a malware sample. Zero-Day exploits are techniques that exploit previously unpatched vulnerabilities, used by attackers to gain unauthorized access to computing systems. While "FUD" may mean "fear, uncertainty, and doubt" in the normal security world, in the underground forum world it means "Fully UnDetectable." On the forums there are "rippers", who are actors identified as ripping off and scamming other users without delivering useful services or contraband.
Luis Mendieta, senior security researcher at Anomali, does an analysis of the common underground marketplaces.