Co-author of the first email program for the Compatible Time-Sharing System (CTSS), one of the first time-sharing operating systems, van Vleck is an American computer software engineer. He worked at MIT on CTSS and in 1965 joined Project Mac, which is the origin of the MIT Computer Science and Artificial Intelligence Laboratory.
Van Vleck worked on the development of Multics for more than 16 years at MIT and Honeywell Information Systems. From 2007, most Multics source code and documentation was provided as free software by IS&T at MIT, a project to which he contributed significantly.
Van Vleck is also known as a computer security expert, and has authored and co-authored several documents. Among these were: "Operational changes for MR 4.0", T. H. Van Vleck, MULTICS OPERATING STAFF NOTE MOSN-A001, Honeywell, April 23, 1976; "The Multics System Programming Process", Van Vleck, T. H. and Clingen, C. T.; Invited Paper, ICSE 1978, pp. 278–280; "Getting the picture; it can be done", IEEE Computer, vol. 27, no. 5, pp. 112, May 1994; "SPMA - Java Binary Enhancement Tool", DARPA Information Survivability Conference and Exposition - Volume II, pp. 152, April 2003; (DOI); Self-Protecting Mobile Agents Obfuscation Report, L. D'Anna, B. Matt, A. Reisse, T. Van Vleck, S. Schwab, and P. LeBlanc, Report #03-015, Network Associates Laboratories, June 2003; and "Anti-Phishing: Best Practices for Institutions and Consumers", Tally, Gregg; Thomas, Roshan; Van Vleck, Tom; McAfee Research, Technical Report # 04-004.
