It's because you didn't ask a full question. If that sort of thing is what you need then no one's going to help you because it'll make them certain you're trying to scam...
If it uses signatures then no it is about as easy to crack as a public key as they normally have 256 bits of entropy applied.
If you think logically, why would a proof of funds ever be hackable if people are happy to provide them?
Ok i just give you a small example
1. The buyer wants to buy 500btc; he provides a bank statement in the amount of 500btc
2. the buyer wants to make sure that the seller has coins in such a volume and requests a satoshi test from a wallet of at least 500 transactions and that it is not a stock wallet
The seller refuses to provide a satoshi test because he is afraid that his wallet will be hacked
from this we can conclude that either the seller does not have coins or the seller is afraid that they can actually crack his wallet