In short: 12-word seed has enough entropy to be safe against brute force attack.
First of all not all 132 bits are random. Seed uses some kind of control sum.
Lets talk about 128 bits of entropy.
Lets imaging the following attack:
We will take one billion (10^9) of the most powerful mining hardware in 2017 (13 TH/s each).
We will make a 1000 years brute force attack to compromise any of existing billion (10^9) of wallets with coins inside.
This attack will check the following number of seed combinations:
10^9 * (13 * 10^12) * (1000 * 365 * 24 * 3600) = ~ 10^33 combinations checked
128 bits of entropy equals ~ 10^38 total combinations
It means the given attack has the following chance of breaking one of more of 10^9 wallets:
1/10^5 = 0.001%
P.S. Don't forget it is an extra complicated task to find out if this or that seed contains any money. Hash mining hardware has much more simple task. We don't have hardware to check seeds at the same rate as modern ASICs.