Just to clarify, MarieC, all anti-virus programs use what are known as 'definitions' that the tell the porgram what is and and what are not viruses.
Because new viruses and security threats are being unleashed all the time, your anti-virus software has to update these definitions so that it can effictively protect your computer from harm.
You message undoubtably relates to the fact that your E-Trust anti-virus does not have an up to date set of virus 'definintions'. As Dafyd says look in the help menu for info on how to update your definitions.