TCPIP Hardware chip & network attatck Answered

Hi everyone.... I like ethernet related project with Arduino and Arduino Ethernet shield.  So now I want to open you a network relate problem. As you know or not Arduino Ethernet shield is made from TCPIP Hardware chip (W5100 of Wiznet Company) and other component. Recently I heard that TCPIP Hardware stack (with Hardware chip) is more stronger than S/W stack from networking attack such as flooding, spoofing and so on. But I want to know technical basis why Hardware tcpip chip is "Unattackable" from networking attack. If there is a anyone have a knowledge about networking via internet... please share your knowldege or your thinking.