A disgruntled network administrator pleaded not guilty Thursday to charges of computer tampering for allegedly setting up an unauthorized access system and holding much of the city of San Francisco's computer network hostage.Terry Childs, 43, entered the plea in San Francisco Superior Court on Thursday morning. His next court appearance is a bail hearing set for July 23.Administrators have been struggling for the past few weeks to regain control of the city's Fibre WAN (wide area network) after Childs allegedly reset administrative passwords to its switches and routers, and refused to hand them over.This network, used to connect computers between buildings throughout the city, carries about 60 percent of the network traffic of San Francisco's city government. It has continued to function normally, but without administrative access the city can no longer make important security and configuration changes to the hardware.Childs is a network administrator with the city's Department of Telecommunication Information Services, which runs the city's critical IT operations, including the e-mail system, Web site, 311 call center and telecommunications infrastructure.He became erratic and then hostile with colleagues after a recent security audit uncovered his activity on the network, according to a source familiar with the situation.Childs is being held on a US $5 million bond, an unusually high amount for a computer tampering case. He faces seven years in prison if convicted on all counts.The city is now working with Cisco Systems to repair the problem, but if it has to replace the routers and switches that have been tampered with, it could easily face a $250,000 bill for the incident.San Francisco began rolling out the Fibre WAN about four years ago as a less-costly alternative to leased data lines. The city has spent more than $3 million on the project.