I've honestly always felt that agents - however they're called in whatever edition you're in - were one of the ways to seperate the hackers from the wannabes. Wannabes might buy a dumb frame or two, and basically remote-pilot them kamikaze-like into the action; it's the delicate, fine programming of a smart frame / agent / bot / whatever that enables a hacker to spread his digital fingers wide and get deep into the guts of whatever he's trying to do. There's just too much that's out there for a decker to personally have to interact with.
And that, functionally, is the second part of it - an agent, a 'smart frame', is going to be programmed to take cues from the decker's own actions, code phrases, and the like. Should it run on the decker's own deck? I'm of two minds on that one - I think that if you run it (or all of them) on your deck, you should have instantaneous access to anything they snag, but if they get hurt, so do you. On the flip side, I think that you SHOULD be able to cut them loose, to run on the global network, but then they have to actually come back to you in order to give you the goodies - and if they get roasted, you are none the wiser.
Unfortunately, Data Trails is as likely to have hard rules for coding and the like as Street Magic has rules for building spells. Me, I love crunch, especially that which lets you take something apart (vehicle, deck, weapon, spell) and understand in game-technical terms how it works - and then go and put your own wizzer custom thing (vehicle, deck, weapon, spell) together.
Were I to house-rule something along these lines, I'd simply say that these sorts of programs can't be copied; you can't buy (or code) one version of DataHunter V, copy it a dozen times, and send the dozen copies out into the ether to do your search; the code requires unique identifiers, and copies screw that up, meaning that the matrix is confused about which one is the REAL one, and winds up frying them all into digital dust. If you want multiple agents, you'd have to buy or code them - but then, I'd also require some sort of test by the decker (at least software, presumably) in order to fine-tune the agent, perhaps a Software + Logic [Mental] (3 * agent rating, 12 hours) extended test to get it tweaked in just the right way. That means a wannabe is going to wreck expensive agent after expensive agent, because they'd [ degrade, work in the wrong ways, conflict with the decker's own style/actions/code ], whereas the true decker is going to be able to buy a good Level 6 Mastermind Agent and a few lower-level Thug 4s and get them properly networked - between both each other and himself.
