Read more at https://blog.ark.io/ark-core-series-multisignature-server-9557f5a9e711
Multisignature Server repository available at https://github.com/arkecosystem/multisig-server
Then again, some of these hacks (I'll dare guess that "most of them") are done by the companies themselves... actually they are not hacks!
But a necessity for this system to work in big companies and exchanges is a workaround in case that one of the multi-signature accounts is for whatever reason unable to sign... maybe some lost their key, or they died, or they got hacked and locked out.
Would it be possible to have a multi-signature system where for example 3 out of 5 signatures are required?