A network computer client device (NC) maintains a root internet service provider (ISP) certificate which includes the ISP's public key and which is digitally signed by a root authority using the root authority's private key. The NC also maintains a root public key. When an ISP desires to write onto the smart card inserted into an NC, it sends ISP account information to be written including a digital signature portion created with the ISP's private key to the NC. The NC performs a cryptographic verification of the ISP account information using the ISP's public key found in the root ISP certificate. If this verification is successful, the NC writes the ISP account information to the smart card. If this verification fails, the ISP account information is not written to the smart card. When an ISP attempts to read ISP account information from a smart card inserted into an NC, the NC first authenticates the ISP The NC then reads the ISP account information including the digital signature portion from the smart card. The NC performs a cryptographic verification of the ISP account information using the ISP's public key found in the root ISP certificate. If this verification is successful, the NC transmits the ISP account information to the ISP. If this verification fails, the ISP account information is not transmitted.