Protip: set up a Google alert for the name of your app and, if your app is particularly popular, the name of your app + “crack” and you’ll occasionally find a site with a cracked version of your app for download, often under the guise of some form of public service to promote “try before you buy.”

Each and every time I’ve caught someone pirating any application I’ve been involved with, something similar to the following has been sent to their domain registrar and to whatever contact is available on their whois record as well as through any contact means that they choose to put on their site.

Dear Sir or Madam

We are the proprietors of all copyright in a software application 
entitled superFroozleApp (The "Work"). We have reserved all rights in 
the Work, which was first expressed in material form on the Apple iTunes 
Store on January 1, 2010.

It has come to attention that our work has had its Digital Rights 
Management removed, has been uploaded to your web site, and is available 
at http://www.somepirate/superFroozleAppForFree.html. Permission was 
neither asked nor granted to reproduce our Work and your hosting of this 
Work therefore constitutes infringement of our rights. In terms of the 
Copyright Statutes, we are entitled to an injunction against your 
continued infringement, as well as to recover damages from you for the 
loss we have suffered as a result of your infringing conduct.

We demand that you immediately:

1. remove all infringing content and notify us in writing that you have
done so;

2. immediately cease the use and distribution of copyrighted material;

3. undertake in writing to desist from using any of our copyrighted Work 
in future without prior written authority from us.

We await to hear from you by no later than close of business, 18:00 
Eastern Daylight Time on Friday, June 25, 2010.

This is written without prejudice to our rights, all of which are hereby 
expressly reserved.

Yours faithfully,

Jonathan A. Saggau
President Enharmonic (Copyright holder of superFroozleApp and
t: +1 555.555.5555

A little web searching can find the various free cease and desist templates I used to cobble that together. Most of it is here.

How often does this work? For me, so far… Every. Single. Time. No Kidding.

There have been a couple of instances of a site owner trying to convince me to “partner” with him or her to “market” the application, to which I respond with a canned letter like this one.

Hello xxx

While I agree that the app store is in need of the ability to try before 
you buy and I like the idea of potentially distributing trial 
applications outside of the app store, I cannot agree with your methods.

By removing the Digital Rights Management from iPhone Apps and 
distributing them without permission of the copyright holder, you are
committing an illegal act.  I suggest that you cease this practice and 
instead contact the developers for permission so that they can make an 
informed decision whether to partner with you.  It is unlikely that an 
informed developer would do so as it runs afoul of their agreement with
Apple.  I have chosen not to partner with you, in part because I cannot 
trust you based on your past actions.

Thank you for removing our application from your site.  Please do not 
post it again in any form.

Having the text above in my back pocket has proven quite useful and makes it easy to police some of the “fringe” use of my work without too much effort. It’s amazing to me how effective these two little bits of text have been so far. Feel free to use and modify at will.

I’m not a lawyer; this isn’t legal advice; caveat reader;