I'm sorry, but running userland "daemons" is child's play. This has been around for EONs. Please don't think you have something new here.
You problem here is that, you idea will only affect the *USER* environment, not the machine. Anything you run or install into the user environment will be bound by the standard user accounts everyone should be running as, without privileges (such as root/super user)
This separate the privileges from the user and the system quite well and delineates it.
Lets compare Windows and *NIX (in general):
Windows, I can send you and e-mail and you standard user just looks at my e-mail and via ActiveX can leverage a 10 year old exploit to install a service as a *SYSTEM ACCOUNT*. This means my process then has full access to the system... Possibly being able to wipe out the machine period, or use it for a launching pad to send out e-mails to other accounts on the system or other account in any address book or just grab your passwords (probably being abcd1234 or password or or what have you (Think Sarah Palin's Yahoo account... wooo really good password there)) for your Bank account. Its very much *THAT* simple, no stupidity involved.
Now, if for some reason ActiveX is disabled, I can just tell you how important the Microsoft update is and it needs to be run... and how you *MUST* forward it to your friends so they can be safe... Sheeple are gullible and will never be safe from this stupidity.
Now speaking of stupidity, its really the only way Linux/*NIX/*BSDs will be compromised... even then most likely only the *user's* data will be flogged. Not the whole system. Now, let us just say *I* download and run your program/update/shell/python script/perl script/etc... Sure it downloads and installs the BOINC daemon and runs in the background... to be honest who cares. Any program you run or have running to capture data from the user will only affect the *USER* not the whole system. Separation of privileges is pure and simple why the *NIX systems will not seriously fall prey to these kinds of things. And to be honest, unless you install a persistent AT job for the BOINC daemon to start or at the very least a cronjob that runs every minute... a reboot will kill your pitiful attempt.