In Ghost in the Shell: Stand Alone Complex series, the modular delayed action virus is mentioned quite often. Is there any explanation for what it actually is or does?
A modular delayed action virus is nothing particular. It's a virus, that is uploaded and takes action later, with a modular design, which means, that it's kind of generic, so it can be modified easily.
The term is used quite often, because different characters use such viruses very often - So there's nothing someone could say about "what it does".
I know this question was asked long ago, but I feel that the answer given is not what the asker was looking for.
I pulled this information from a rulebook online for a D20 pen and paper adaptation of Ghost in the Shell to the Dungeons and Dragons roleplaying system.
Here is the website: http://www.serenadawn.com/GITS-InformationAge.htm
Modular virus: Similar to Toy Bombs, They are disguised in e-mails or picture file header data, and when certain conditions are met, they compile into a single program. In the 'Laughing Man' attack on the Superintendent-General, one of these was slipped into the security detail and stored inside their cyberbrains. The Modular virus finishes its attack profile and then transmits itself to another target, usually the same type. The programmer uses up one slot in the portfolio, detailing the target and the range from the previous one. A modular virus can, for example, target all robots in a factory but only those. It will continually attack the target and not move onto the next one until the first one is finished.
I hope this is what the original asker was looking for.