std.cpp definition, relationships, removal:

The std.cpp file is an essential part of a particular parasite and therefore is responsible for the pest's malicious activity. Exact purposes of std.cpp depend on the related parasite's type and carried payload. Some threats can use std.cpp to serve annoying pop-up advertisements or store certain configuration settings, while others need it to corrupt files, steal user confidential information or run a spreading routine. In any case, DO NOT open this file!
The std.cpp file is installed and used by keylogger Nano.
Sometimes a presence of std.cpp does not indicate that your computer is infected. It can be an essential system file or a file installed by harmless legitimate software and therefore may not pose any threat to your privacy and the system. Although such cases are quite rare, you should thoroughly examine std.cpp before completely deleting or leaving it in the system.