I tried to upgrade from Joomla 1.5.23 to 1.5.26 by following cPanel-specific instructions at http://docs.joomla.org/J2.5:Migrating_from_Joomla_1.5_to_Joomla_2.5#Review_the_Requirements
which referenced
http://docs.joomla.org/Uploading_and_extracting_an_archive_file_with_CPanel
I downloaded patches from
http://joomlacode.org/gf/download/frsrelease/16891/73384/Joomla_1.5.0_to_1.5.26-Stable-Patch_Package.zip
and
http://joomlacode.org/gf/download/frsrelease/16891/73386/Joomla_1.5.25_to_1.5.26-Stable-Patch_Package.tar.gz
When I tried to upload
Joomla_1.5.0_to_1.5.26-Stable-Patch_Package.tar.gz
or
Joomla_1.5.0_to_1.5.26-Stable-Patch_Package.zip
I get an error message from cPanel which says
C:\fakepath\Joomla_1.5.0_to_1.5.26-Stable-Patch_Package.zip: unknown Bytes complete FAILED! :Upload canceled: VIRUS DETECTED! (Access denied. ERROR)
I do not know if there is a virus in the patch (which would be really bad!) or if there is some bug with cPanel. Given how scary a virus in the patch is, I figured I had better report it.
I'd suggest downloading the packages fresh from the site again and checking them with a local virus scanning tool in before trying to upload again. Considering how old 1.5.26 is at this point, it's somewhat doubtful that there's only now a virus in those packages.
Also, this repository is for the Joomla! Issue Tracker application. Your issue pertains to the Joomla! CMS, please report it at https://github.com/joomla/joomla-cms/issues/new