Cloaking
Cloaking is a skill that goes hand in hand with scanning. Cloaking modules are researched via the Research Tree and have various uses. Cloaking is essentially 'Scanning Defense'. It protects against hacks as well as being a requirement for hacking. The Zolazin get a boost to cloaking, as do Spies, so Zolazin Spies get a huge boost.
Cloak is also used to protect planets. A heavily cloaked planet is less likely to be scanned by another player.
See also Cloak, Jammers and Cloaking Modules