The following information summarizes how macro (macro: An action or a set of actions that you can use to automate tasks. Macros are recorded in the Visual Basic for Applications programming language.) virus protection works under each setting on the Security Level tab in the Security dialog box (Tools menu, Macro submenu) under different conditions. Under all settings, if antivirus software that works with Microsoft Office 2003 is installed and the file contains macros, the file is scanned for known viruses (virus: A computer program or macro that "infects" computer files by inserting copies of itself into those files. When the infected file is loaded into memory, the virus can infect other files. Viruses often have harmful side effects.) before it is opened.
Security Because macros can contain viruses, be careful about running them. Take the following precautions: run up-to-date antivirus software on your computer; set your macro security level to high; clear the Trust all installed add-ins and templates check box; use digital signatures; maintain a list of trusted publishers.
Low
When security it set to low, all macros are treated equally, regardless of origin or certificate status. With low security, you receive no prompt or signature validation, and macros are automatically enabled. Use this setting only if you are certain that all macros in your files are from trusted sources.