A great number of previous versions of Sendmail have known security holes. Check installed sendmail for the most recent version. Alternatively, consult the operating system vendor to get the most recent release for the platform. Remove any script that is not needed in the course of operation of a web server. Examine log files on the host frequently.
Good backups are the best defense against system damage.
Perform backups before placing a system on the trade show network then continue backups throughout the show and again following the event. Most are exhibitors who have a legitimate need to run them during the course of product demonstrations. Particularly prone to eavesdropping are telnet sessions. As mentioned previously, authentication tokens and ssh are a simple way to add security to system account access. Many routers support basic packet filtering.