Virus hoaxes are usually email messages warning of a virus and telling users not to open a specific email or take other action, or they will get a virus. Hoaxes waste vast amounts of time and bandwidth as they are passed from user to user. In some instances they can be more malicious, eg: if they tell users to delete a system file which is required for correct operation.
You cannot get a virus by reading email messages, but you must be careful of files attached to email messages, because if the file is an executable program, Word document or other file capable of being infected with a true virus, it may have a virus in it.
The best way to deal with virus hoaxes is to reply to the source of the message and tell them politely that the virus warning is a hoax. You might also want to suggest that in future they should check any virus warnings they receive against one of the web sites listing virus hoaxes, before forwarding warning messages, eg:
CIAC Internet Hoaxes web page at http://ciac.llnl.gov/ciac/CIACHoaxes.html
Symantec Hoaxes Page at http://www.symantec.com/avcenter/hoax.html
Next: Infection Mechanisms