tl;dr: In 1996, id Software released a Quake shareware CD-ROM that also contained encrypted versions of their full game catalog, unlockable via a phone-in payment system powered by TestDrive Corp's software. The scheme was cracked in 39 days by hacker group GNOMON, who discovered the "unlock code" contained no server-side secret—the local FLOW.EXE could generate valid serials itself from the challenge code, relying purely on security through obscurity. The CD was riddled with additional flaws, including unencrypted plaintext copies of "encrypted" databases and a typo that broke legitimate Final DOOM unlocks, leaving id with 150,000 unsold CDs.