Reading data from memory that's being used by another program.

[Theo Paphitis]

Is it possible to read data that's being stored in memory from another program?

If I'm correct isn't this how game hacks work? (Never used/written one only read up about it).

[Athar]

Yes, it depends on the OS. It can be done with ReadProcessMemory on Windows and by reading from /proc/pid/mem (or using ptrace) on Linux.
You have to be admin/root to do this, though.