Demo

Direction

1. File > New > 100x40 pixels with white background.

2. Press D.

3. Go to Filter > Noise > Add Noise > use this settings.

4. Now you got something like this.

5. Go to Single Row Marquee Tool > click at the top of your document > press Ctrl + T.

6. Pick one square and drag it down to the bottom of your document.

7. Done.