If you're a tinkerer or a hacker, a tool as just popped up on our radar that could be of interest to you. SIS Editor allows you to tweak the contents of .SIS and .SISX files. There are legitimate reasons to do this, such as working around app store related bugs. However, I wanted to bring this to everyone's attention for another reason. This application makes it easy for someone to write a malicious application masquerading as another app entirely, and distribute as a self-signed application.
The reason for posting a link to this application is not to encourage its use, but to highlight it as a cautionary note about installing applications from unknown or untrusted sources. Symbian makes it very easy to 'sideload' applications, which many users have appreciated at one time or another. This freedom comes at the cost of increased (potential) risk.
This application shows that the tools are out there for anyone to use, so please be careful where you are sourcing your applications from, and unless you have a good reason not to, stick with downloading from the Nokia Store.