Trojans are malicious applications that pose themselves as legitimate software in order to trick users to install them. Once on the victim's machine, it may run any number of malicious process to steal vital information or inflict damage to other software.
Nickser is a backdoor trojan program. The trojan itself is a Windows PE EXE file about 136KB in length. It is written in Microsoft Visual C++.
When run the backdoor copies itself under the name lsass.exe name to the Windows directory and registers itself in the system registry auto-run key: