FortiGate
FortiGate Next Generation Firewall utilizes purpose-built security processors and threat intelligence security services from FortiGuard labs to deliver top-rated protection and high performance, including encrypted traffic.
Lovepreet_Dhillon
Article Id 267999
Description This article describes a workaround for FortiOS 6.4.4 when it is not available for download. 
Scope FortiOS.
Solution

FortiOS version 6.4.4 has been removed by the Development team and soon will be removed from the upgrade path.

Meanwhile, FortiOS 6.4.4 can be skipped during the upgrading process.

 

Example:
While upgrading FortiGate 90E from 6.2.15 to 6.4.12, the upgrade path tool will show the following path:

Version Build Number
6.2.1>6.2.3>6.4.2>6.4.4>6.4.6>6.4.8>6.4.10>6.4.12

 

While following the above upgrade path, it is safe to skip 6.4.4 and upgrade to 6.4.6 from 6.4.2 directly, then follow the rest of the upgrade path.


Related document:

Upgrade Path Tool Table.