PerfectNav is an adware hijacker.  PerfectNav will redirect your search queries and mistyped URLs over to their website. PerfectNav also has the ability to monitor your Internet activity and as a result will send targeted advertisements to your computer.  PerfectNav will also take over your Internet Explorer settings and change your homepage without your permission.
PerfectNav is junk software and was probably installed as part of a bundled software package.  It is highly recommended that you remove this problem from your computer as soon as possible.  Not doing so will result in damage to your computer and more vulnerability to additional spyware.  SpyZooka, a trusted anti-spyware program, is an excellent choice for removing spyware.