I delete the gbas.so file from my home directory but it keeps coming back. Where does it come from?
As mentioned by nelaar, ".so" files are usually shared binary libraries. Try doing "readelf -a gbas.so", it might give you some information about what the file contains (if it really is a library file).
It is related to the safety solution of Banco do Brasil. The java applet downloads these files everytime you access your homebanking.
Open up Synaptic package manager and search for this file to see which package does this belongs to.