If you run a website on Joomla you may be aware of the different versions of the software that are available (1.5, 1.6, 1.7, 2.5, 3.0). Joomla only supports the most recent versions of the software with patches and updates, for example the latest release of 2.5 at the time of writing this article is 2.5.8.
The Joomla release cycle includes Long Term Support (LTS) releases which are supported for 21 months (current LTS is 2.5) and Short Term Support (STS) releases that are supported for 7 months (current STS is 3.0).
Joomla 1.5 reached its end-of-life on 30 April 2012, and should be replaced with 2.5. If you are running Joomla 1.5 then we strongly recommend updating to the latest version of this release (1.5.26) and then migrating to Joomla 2.5.
We understand some users may not be inclined to migrate due to financial or time constraints, or for accessibility reasons. As Joomla 1.5 is no longer supported by the developers security updates are no longer available which makes the 1.5 release vulnerable to hacking. If you wish to add extensions to your existing site you may have difficulty as the Joomla extension developers are now only supporting releases 2.5 and 3.0.
If you stick with 1.5 your website will continue to work just as before however it will no longer be considered secure. If a hacker finds a weakness in Joomla 1.5, he or she will be able to exploit it, since the developers won’t provide any more security updates. But this might not happen and the system could remain stable for years.
HostAway’s Joomla version monitoring (which alerts you if the version you are running is outdated) now considers 1.5.26 to be outdated. We want you to be aware of the risks but ultimately you have to decide whether or not it’s more advantageous and cost-effective to migrate to 2.5 now, even if that entails additional expenses, than to stick with 1.5.
If you’re still keen on remaining with 1.5, then we suggest improving your website security as recommended by Joomla here.