Lightning Bug

Lightning Bug is an active defense program. The program creates 6 motes of light that slowly circle the Netrunner. If any program comes within I grid space, one of the Lightning Bugs will immediately launch itself at the program. If it's successful. it will inflict 2 points of damage. The Lightning Bugs will each attack one by one until there are none left or the program has been de-rezzed.

The advantage of Lightning Bug is that it is a defense program that doesn't need to be operated every turn. once you first run it and summon the Bugs, you don't have to bother with it from then on. You can focus on other programs while the Bugs are doing their thing. Note: once all 6 Bugs are gone. you must leave the Net and re-boot the program to activate it again.

Source

 * Rache Bartmoss Guide to the Net, pg.148