can lock handcent but not stock text app

[are we there yet]

Hi

I downloaded handcent and have a pin code to lock it.
However when I click on apps, stock text message app, it allows access.

I cannot disable app, as it is greyed out.
How to I lock this app too!
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[m@tt]

I have used this in the past

https://play.google.com/store/apps/...=W251bGwsMSwyLDEsImNvbS5zZWJhc3RpYW4uc2VhbCJd