Learn how to acquire and apply vendor patches to your operating system and applications.
Use an available secure system to download patches to apply to a new Unix installation.
Verify software with PGP signatures. Make sure you obtain the author's PGP key from a trusted source (or multiple independent sources).
Check the MD5 checksum of downloaded software.
Read mailing lists that publish general security announcements.
Read mailing lists devoted to your vendors ' products.
Consider when and how you will back out a patch that doesn't work.