Compatible printer cartridge retailer's know full well that their products are not always 100%, and leaks do occur. I know for sure that I have experienced leaking compatible cartridges in the past, and have had refunds to prove it.
A word of warning, you may never be able to remove mess or the stains, after this incident. Spilled ink a terrible commodity to remove, especially on plastic.
Why not seek advice from Consumer Direct click here about your legal rights in a situation like this. It might also pay to contact PC World's main customer service, and see what they offer!.