They usually arrive in e-mail attachments or when you copy software or files from remote Internet sites. CERN's virus protection software will normally detect them and warn you automatically. Nearly all the warnings about viruses that come by email are hoax, particularly when they ask you to forward the e-mail to others. In general you can ignore these e-mails or check their validity by searching this uptodate list of hoax and viruses. For System administrators CERT security advisories are official notifications of security problems.
CERT is a body in the U.S. which handles security incidents.
Their web site can be searched for security vulnerabilities and fixes. Other bodies also issue security warnings and alerts. Guidelines for configuring anonymous ftp , information on typical anonymous ftp abuses and other technical security advice is available in the Tech Tips section of the CERT web site. Security information for CERN author's of CGI scripts is here . Web servers must be regularly updated with the latest security patches.