Actually, being cans they shouldn't be skunky but rather wet-cardboardy. Oxidized (ie: old/stale) beer developes a wet cardboard aroma & flavor. The skunky aroma is a characteristic of lightstruck beer, the photonic energy breaks down the iso-alpha-acid (what gives beer it's bitterness, developed when the alpha acid from the hops is isomerized during the boil), one of the components of the photonic breakdown is the skunk. Brown glass pretty much prevents lightstruck beer, green glass only gives you 10 minutes or so of protection, clear glass is useless (think Corona) with the exception of Miller products. Miller wanted clear bottles so bad that, with typical American ingenuity, they developed a way to chemically alter the hops & stabilize the iso-alpha-acid bond.