隨著各種網路技術與生活的結合，行動無線上網不受時空限制的便利，因行動業者3G及3.5G HSDPA高速服務的陸續推出而更趨熱絡，然而在以量計價的上網計費方式中，隱藏於GPRS網路中的惡意攻擊GOA(GPRS Overbilling Attack)，不僅使得用戶之上網費用暴增，更引發使用者對業者的計費方式產生質疑與紛爭。本文主要介紹 2/3G GPRS 網路之系統架構包括網路架構及其網路設備元件， GOA 攻擊方式及防範 GOA 攻擊的方法等相關議題。然而，在現今 2G 與 3G GPRS 網路互聯運作之情況下，如何慎選防範機制且能相容運作於兩大系統之間，則是本文最後探討未來對 GOA 的防範工作與願景。 With the integration of various kinds of network technologies into our daily life, the convenience of mobile internet access is getting more and more popular with the launch of 3G and 3.5G HSDPA by operators. Nevertheless, the way of charging by quantity of packets for net surfing via GPRS network is vulnerable to intruders who attack the subscriber intentionally. The result of GOA attack makes the network expenses on users increase suddenly and violently. Furthermore, it can cause disputation and untrustworthy issue between subscribers and operators. In this paper, the architecture of 2G/3G GPRS network and the network elements will be introduced. The way of GPRS Overbilling Attack (GOA) in 2G/3G network and method of prevention are mainly discussed. We also need to consider that which way of prevention is better and suitable for both 2G and 3G networks. Whether the attacks against GPRS systems would become a problem in the future, how to prevent subscribers from the GOA attack is truly an urgent issue from now on.