This technique of infecting things as they are used is one of the features that most of the currently-common viruses share.
Shared machines are therefore one important place to apply virus protection programs.
If such a diskette becomes infected, the infection can quickly spread to many machines. Programs on LAN servers should be carefully checked for viruses, and LAN access controls for shared programs should be set up correctly. In general, the most reliable symptom of a computer virus is an alert from a good anti-virus program. The 1813 virus is actually one of the more obvious of the common PC-DOS viruses. But in any case, checking a malfunctioning computer for known viruses with an anti-virus tool is generally a quick and easy process, and a useful addition to a support person's toolkit.