* Treat public-domain and shareware software with caution. Before running it, check its health with a virus-detector scanning program. Viruses cannot replicate until the program they have infected is executed.
* Scan even commercially acquired disks; contaminated software can be inadvertently shipped directly to customers.
* Newly acquired software applications should be backed up immediately. Execute programs only from backup copies or from a hard disk, thus ensuring that unaffected disks are available should working copies become damaged.
* Make regular backups of customized files. If they're attacked, you'll save hours in rebuilding the system.