Anonymize names - sort of Edit: There will be a bonus of -20 for random masking

Hello fellow Whistleblowers and carriers of secret knowledge.

I am due to an interview by mail and I - of course - cannot say specific names in full length. But as I want to disclose it in a rather not-so-obvious-way I need your help.

I will provide these names in the form of 


  "evil_company_that_makes_me_shiver"


but surely I do not want to spell it out completely. Your task to help me and the whole world is that you provide a nice program that turns the above into

"ev**************************"


or

"**il************************"


or even

"****_c**********************"


I think you get it. But there is one flaw: I want to disclose the name in total, so I need to pass the number of occurrences and the word itself to the script and it will disclose the letters bit by bit. An example could be

~$ ./whistle NSA 3
&gt; "N**"
&gt; "**A"
&gt; "*S*"


or

~$ ./whistle nuclear 3
&gt; "nu*****"
&gt; "***lea*"
&gt; "**c***r"


or

~$ ./whistle nuclear 2
&gt; "nuc****"
&gt; "***lear"


I hope you can help me and as we know that size matters the shortest code wins. Help make this world a better place!
GolfScript, 26 charaters
Since no specific way of disclosure was specified I decided to go for the shortest:
:f,\`{{\)f%.!@42if}%\;n}+%

You may experiment with this code online.
Example:
&gt; &quot;ABCDEFGHIJKLMNOPQRSTUVWXYZ&quot; 7
******G******N******U*****
*****F******M******T******
****E******L******S******Z
***D******K******R******Y*
**C******J******Q******X**
*B******I******P******W***
A******H******O******V****

Commented code:
:f           # Save the second input to variable f
,            # Makes the array [0 1 2 .... f-1]
\`{          # \´{}+% builds a code block where
             # first the input string is pushed (done
             # via the + operator and afterwards the whole
             # block is applied to above array, i.e.
             # For each line 0, 1, ...                                                
             #   Here, the stack contains the line number (counter)
             #   and the string
  {          #   {}% -&gt; map to each character of the string
             #     Stack contains counter and current character
    \)f%     #     Increase the counter by one and calculate modulo f
    .        #     Duplicate counter (will be used for the if below)
    !        #     and test for zero 
             #     I.e. if counter==0
    @        #       Then Current character
    42       #       Else 42 (which is '*')
    if       #     
  }%         #   The mapping operation masked most of the characters
  \;         #   Discard the counter
  n          #   Add newline
}+%