Step 1

 Begin with a new file, 100x100, with a transparent background. Then set your background color to white #FFFFFF and your foreground color to #ff0000.

Step2

Now go to Filter>Render>Clouds, and now should it look something like this.

 

Step3

Then go to Filter>Pixelate>Mosaic and set the Cell Size to 15.

Step 4

Now go to Filter>Sharpen>Sharpen, and then repeat this step a couple of times (4-5).

And that's it your done!

This is what I came up with