A conduct committee of the General Teaching Council for England found facts surrounding John Jenkins' dismissal amounted to unacceptable professional conduct and issued him with a conditional registration order.
He was sacked from Ridgewood high school in Wollaston, Stourbridge, West Midlands, in November 2001. No details of the dismissal of the "highly-regarded" teacher were revealed and the GTCE hearing was, for the first time, held in private.
Sue Bates, headteacher, told a local newspaper that Mr Jenkins had irretrievably breached the school's trust.
The GTCE hearing issued the conditional registration order after three hours' deliberation. The order means Mr Jenkins can remain in teaching if certain conditions are met.
Anne Madden, chair, said the committee was satisfied the facts of his case amounted to unacceptable professional conduct.
It had taken account of mitigating circumstances, but she said: "Any school employing Mr Jenkins must have sufficient means to prevent computer misuse.
"Internet access must be monitored and any inappropriate use be reported."