_setup.lib definition, relationships, removal:

The _setup.lib file is an essential part of a particular parasite and therefore is responsible for the pest's malicious activity. Exact purposes of _setup.lib depend on the related parasite's type and carried payload. Some threats can use _setup.lib 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 _setup.lib file is installed and used by trojan BackFire 1.31. It is also related to other parasites such as trojan Backwork, Dcide Privacy Companion, Khe Sanh, Matrix (Maverick), Net Administrator 1.0 and SPAM Relayer. These threats can use _setup.lib for different purposes, as the file's functionality depends on a particular parasite it belongs to.
Sometimes a presence of _setup.lib 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 _setup.lib before completely deleting or leaving it in the system.