Inline assembly manipulates values without cleaning higher-order bits or without overflow checks, so masked types (address, bool, small uints) carry garbage bits that corrupt comparisons and storage.
assembly {
let a := and(calldataload(4), 0xffffffffffffffffffffffffffffffffffffffff)
}
Largest recorded losses in the same failure class — related, not the same bug:
The SaferICO scanner runs 201 detectors over your Solidity source, SAFE-0031 among them. Paste an address or the source itself — a small per-scan fee, shown before you sign, or unlimited on any plan.