You need to install the SILC Toolkit and the libpurple SILC plugin. These were generally provided as packages in several Linux distributions, however, many distributions have begun dropping these packages due to being "unmaintained." If you're compiling Pidgin and libpurple yourself, see the
`./configure --help` for specifying the location of the SILC headers and libraries. If you're compiling with an SRPM, use
`--with-silc` to build the
`purple-silc` RPM