Oxidation of an organic compound (like burning) tries to put every atom in its highest oxidational state. We can say when something like methane, (C -4, H+1) is burned, we get CO2 (C +4, O -2) and H2O (H +1, O -2).
When we burn chloroform, CHCl3 (which doesn't burn so good as the C is already +3), you could still say that the Cl can be oxidized up to +7. It yields ClO4-.
What i mean with the + and - a number, i give the oxidation state of that particular atom. I know this analogy is wrong when looking at covalent bonds, but it is a good way to explain these things.