I make my art using Pixlr.com. What I do for the glitch effect is to draw a bunch of tiny multicolored squares (using the paint tool) on a separate layer (sometimes putting two different-colored squares right next to each other. Then I go to the Filter header and play around with the Glitches>Fringes or Slice settings, and/or Effects Library>Mosaic (usually a mix of both settings) until I get it looking right.