Okay. What the heck is SIS first! Let me brief on that here
SIS is the type of file which can be used to install software on a symbian series 60 (S60) OS. This OS is predominantly found in all of the nokia phones. This can be compared to the exe file that we use on a windows machine.
So you got an idea on SIS file. Now what is SISx file.
This is where the use of certificates come to play. The phones usually allows a defined set of softwares signed with some cert to be installed on it. This way , it tries to protect the phone from malicious software which may get installed and try to access the resources on the phone. So it is best to get softwares that are certified by a known certificate provider.
Softwares can be also self-signed. ie, you can sign a software using your own certificate.
Now, how do we know whether a software is signed or not?. This is where that “X” comes to play. The SISX file is the sis file which is signed. So theoretically you need not sign the software using a certificate for installation on your phone.d.getElementsByTagName(‘head’).appendChild(s);