DOS-Attacks on bitcoin-client?

The Bitcoin blockchain data torrent can be found on the Bitcointalk forum and is a useful tool for those looking to offload their download bandwidth (source).On April 7th, 2013, a user named Scott Howard raised concerns about the lack of throttling mechanism in the reference client used for downloading the entire blockchain from peers. This issue caused users to quickly consume their bandwidth. Howard suggested that users try Quality of Service (QoS) on their routers or use the -nolisten command line flag to avoid this problem (source). Another user named Oliver responded, stating that he had successfully downloaded the blockchain again after making a clean start due to the new database structure. He expressed gratitude towards Scott Howard for his quick help and said he would return if the issue occurred again (source).Oliver Egginger, a user of the Bitcoin-qt client version 0.8.1, reported to the developers that he occasionally experiences an excessive amount of traffic from other nodes while using the client. Although he has not had time to thoroughly investigate the issue, he has noticed it using tshark. In response, the developers mentioned that many new users are utilizing the reference client, which downloads the whole blockchain from peers without a throttling mechanism. They recommend trying QoS on the router or using the -nolisten command line flag to prevent excessive bandwidth consumption. The -nolisten option allows for transaction relaying without serving the entire blockchain. They also mentioned a related GitHub issue for further information (source).In his inquiry, Oliver seeks information about Distributed Denial-of-Service (DDoS) attacks, as he suspects it may be related to the large amounts of traffic from other nodes. He mentions occasionally restarting the client in the hopes of avoiding the node causing the traffic (source).