In our office we encountered strange issue.
Our xerox 3610 printers every hour (+-) print two pages, which have printed % - 12345x chars in top left corner.
We use Windosw 7 Pro with SP1,windows is up to date.
Printer's drivers are those delivered with printers on CD - PCL6, connected via USB.
Can You, please, give me some advice how to solve or workaround this issue?
I would guess your IT is running a security scan against the LAN and the printer is printing the code it uses when doing so.