A whole lot of non-text data like:
▒▒V▒*[O
▒~eT,K▒▒,<▒g2▒p▒▒_▒L#Y^~▒»g|▒s▒▒▒{▒▒▒▒▒7▒l▒▒▒▒▒▒۠Nz,▒▒̰`▒
▒▒▒g▒▒ے▒h▒)8▒▒▒▒▒^%▒T▒▒▒4▒⻊▒▒▒C▒ 8▒h▒▒J▒▒▒OVh▒>e.)▒)+կa.▒▒▒▒▒d▒:▒R▒Ǹ▒▒>B▒ ▒v▒▒▒▒~▒ޮ▒▒Y▒+▒▒?▒▒m▒▒g▒▒'▒}%/g▒▒v;▒▒HR|▒kH▒o▒▒Y▒▒▒▒▒▒?▒us▒▒d▒q▒▒oQ▒]▒▒]C▒#n▒p." ▒\
The size isn't exact, but it is similar in size to, a software package. I tried to update the firmware yesterday, which failed due to low disk space, and seemed to trigger the warning I specifited in the original post. The location where I copied the software package to was /var/tmp. The software package is no longer in /var/tmp, but might this be a remant of that failed update?