Trojans, backdoors and droppers are the top three malware types analyzed by Kaspersky Threat Intelligence Portal. Almost three quarters (72 percent) of the analyzed malicious files fell into those three categories. Backdoors are rare in the wild, but backdoors are not as common, only making up 7 percent and 3 percent of all malicious files blocked. Backdoors on Linux and Android operating systems are of interest for security researchers, but their levels are relatively low in comparison to threats targeting Microsoft Windows.
Source: https://threatpost.com/trojans-backdoors-droppers-most-analyzed-malware/157134/