Ignore those DoS log msgs. They are generated by 1 of the PCs on your own LAN.
I get the same whenever my Vista laptop powers on, but not my XP PCs. I don't know the cause but I do know my Vista PC is safe and OK, so I just ignore them.
Yes, Orange support is abysmal. The have no BB expertise beyond "swap filters and reboot router" and are forbidden to employ their brains. Obviously their training is vastly lacking. No point prolonging a complaint with them, certainly not outside their formal written Complaints process; you'll get nowhere and give yourself grief.
1999: Freeserve 48K Dial-Up => 2005: Wanadoo 1 Meg BB => 2007: Orange 2 Meg BB => 2008: Orange 8 Meg LLU => 2010: Orange 16 Meg LLU => 2011: Orange 20 Meg WBC