This is quite a common concern for a lot of people who don't understand the sheer vastness of the "keyspace" being generated by this "fixed and known" list.

People will quite happily secure their online banking or whatever with a 10-12 character password... if you use UPPERCASE + lowercase + numbers... that's 26+26+10 = 62 possible characters... then we can throw in the 33 ASCII printable "symbol" characters like ~!@#$%^&*()_+ etc... and all up it would be 62+33 = 95 characters in your "fixed and known list".

So, a 12 character password using this list would be: 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 * 95 = 540360087662636962890625 possibilities.

The 2048 word list that Electrum uses means that your "alphabet" has 2048 characters... so that means your 12 word seed is effectively a "12 character password where the alphabet has 2048 characters" in it. Giving up this many different seeds: 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 * 2048 = 5444517870735015415413993718908291383296 possibilities...


If you're not worried about someone hacking your 12 character password, you don't need to be worried about someone hacking your 12 word seed.