apt-get questions

out of hundreds of packages installed after restoring from a default 9.0 I have these unsigned packages Checking GPG signatures... Unsigned /var/cache/apt/archives/mozilla_1.6-100.SuSE.ulb.2_i586.rpm Unsigned /var/cache/apt/archives/mozilla-mail_1.6-100.SuSE.ulb.2_i586.rpm Unsigned /var/cache/apt/archives/mozilla-spellchecker_1.6-100.SuSE.ulb.2_i586.rpm Unknownsignature /var/cache/apt/archives/perl-HTML-Parser_3.28-53_i586.rpm The following packages have been kept back XFree86-Mesa XFree86-server gimp2 gnome-icon-theme How can I determine why these packages were kept back?