I use Kubuntu Edgy and have recently noticed a file called 'core' appear in my root directory. It is a binary file. I had recently upgraded to feisty but then went back to edgy.

I have no idea what this file does and it was in older backups as well.

This machine was attacked online when running feisty and desktop icons removed plus problems with feisty led to format of all but home directories and setting up new partitions and reinstall of edgy. Prior to that I ran SuSE. I'm certain this file wasn't there and am unaware of what created it.

Any help appreciated. No problems with laptop, but that doesn't mean I haven't been hacked, though operating via kubuntu proxy server.

Cheers

It's probably a core dump file. What does file show for it?

A core file will be from a core dump, which is produced when a program crashes. In one of your systems setup files, such as /etc/profile, you may find a line that looks like:
ulimit -c 20
(type in "help ulimit" in the bash shell for a manpage or info bash for more information). This value may be read in from a config file in /etc/sysconfig and then the value used in a ulimit command.

The number is the limit of core dumps in 1024 byte blocks. You can also filter out core files from being backed up. They are only useful when you use a debugger. If you don't plan on doing that, you can even delete it. The timestamp on the core dump might be useful. It will tell you when the crash occurred. Being on the root directory,you know that a root program crashed.

Sorry, when I looked at this core file in konqueror it had the 'bomb' icon and Properties identified it as a crash dump file.