These are often cheats that will result in a permanent IP ban. The official Eternal Lite Client has a unique hash signature that the anti-cheat system recognizes. Always verify you downloaded the client from the official portal.
If you are downloading for (especially Android), you are likely looking at the Eternal Client launcher/pack.
The Tai Xương Eternal Lite Client is a double-edged sword. On one hand, it keeps a beloved, dying game genre alive by making it accessible to players with limited hardware and slow internet. On the other hand, the unofficial nature of these clients makes them a fertile ground for malware and server bans.