mod developers can sue people for not getting permission to use.
this is what was on the minecraft forums on how to protect your mods.
TERMS AND CONDITIONS
0. USED TERMS
MOD - modification, plugin, a piece of software that interfaces with
the Minecraft client to extend, add, change or remove original
MOJANG - Mojang AB
OWNER - , Original author(s) of the MOD. Under the copyright terms accepted when purchasing Minecraft the OWNER has full rights over their MOD despite use of MOJANG code.
USER - End user of the mod, person installing the mod.
THIS MOD IS PROVIDED 'AS IS' WITH NO WARRANTIES, IMPLIED OR
OTHERWISE. THE OWNER OF THIS MOD TAKES NO RESPONSIBILITY FOR ANY DAMAGES
INCURRED FROM THE USE OF THIS MOD. THIS MOD ALTERS FUNDAMENTAL PARTS OF
THE MINECRAFT GAME, PARTS OF MINECRAFT MAY NOT WORK WITH THIS MOD
INSTALLED. ALL DAMAGES CAUSED FROM THE USE OR MISUSE OF THIS MOD FALL ON
Use of this MOD to be installed, manually or automatically, is given to the USER without restriction.
This MOD may only be distributed where uploaded, mirrored, or
otherwise linked to by the OWNER solely. All mirrors of this mod must
have advance written permission from the OWNER. ANY attempts to make
money off of this MOD (selling, selling modified versions, adfly,
sharecash, etc.) are STRICTLY FORBIDDEN, and the OWNER may claim damages
or take other action to rectify the situation.
4. DERIVATIVE WORKS/MODIFICATION
This mod is provided freely and may be decompiled and modified for
private use, either with a decompiler or a bytecode editor. Public
distribution of modified versions of this MOD require advance written
permission of the OWNER and may be subject to certain terms.
ALSO off of minecraft.net
What You Can Do
If you've bought the game, you may play around with it and
modify it. We'd appreciate it if you didn't use this for griefing,
though, and remember not to distribute the changes.
Any tools you write for the game from scratch belongs to you.
You're free to do whatever you want with screenshots and videos of the
game, but don't just rip art resources and pass them around, that's no
fun. Plugins for the game also belong to you and you can do whatever you
want with them, as long as you don't sell them for money. We reserve
the final say regarding what constitutes a tool/plugin and what doesn't.
You can copyright you mods but the overall copyright is unenforceable because (at least in the U.S.) you need to sue for damages, and you need to be able to show those damages. Mods are free anyone can download them so showing monetary damage is almost impossible. You could have a lawyer draw up a cease and desist but that would cost a lot of money and for very little gain.
You could create a lawsuit that stated, this guy had his modpack that I didn't give permission to use and he got x downloads that denied me x amount of site ad revenue. However you still would need to prove that A. that without the mod pack the people would have come directly to you and downloaded it, and B. the about of revenue you got from ad's is guaranteed and it isn't because of ad block, no script and other programs.
I don't know the accuracy but according to Kakermix the only mods that have refused to give permission to distribute to technic are buildcraft and forestry and forestry is going to be removed due to incompatibility