Are you looking for Pidgin log files, the free instant messenger application ? Maybe you want to backup them or delete them securely. Here you can find them on a Debian based system and maybe on other distros as well
For other protocols just substitute yahoo with the corresponding names.
Why is the name of the directory “purple” ? Because Pidgin is a GTK+ frontend to libpurple the core of the IM program.
Tested on Ubuntu 8, 9,10