The recommended way to obtain Quartus II 8.1 Web Edition is through the official Altera (Intel) website. Here's a step-by-step guide:
Instead of searching for risky cracks, there are safer ways to get legacy FPGA tools running: quartus ii 81 web edition crack exclusive
The current version of the Quartus II software also includes final power models for the Cyclone, MAX 3000A, MAX 7000AE, MAX 7000B, The recommended way to obtain Quartus II 8
Using a crack to bypass software limitations can pose risks, including: quartus ii 81 web edition crack exclusive