From "Why SEP does not remove the AT, INF, INI, and Registry keys related to infections" (http://www.symantec.com/docs/TECH158359):
By themselves, autorun.inf files are harmless. They contain no malicious code and cannot cause harm to a system. Our detection engines are focused on actual malicious files. Malicious files using an autorun.inf file to launch itself are detected by Symantec. From a security standpoint there are no protection gaps for customers based on our policies towards autorun.inf.
If the autorun.inf file is pointing to an executable (for example) that you suspect is malicious--one that we are not detecting--then I would recommend submitting that file for analysis.
sandra