WhatsApp introduced Chat Lock a while ago, but version 3.3.10 refines the "Secret Code" feature. You can now set a unique password (different from your phone unlock) specifically for your locked folder. This makes it much harder for someone with your basic phone PIN to snoop.
Assuming you have downloaded the WhatsApp_beta_3.3.10.apk file, follow these steps exactly: Whatsapp Beta 3.3.10 Download
This is the most critical section. Because Beta 3.3.10 is not a wide release, you cannot find it on the Google Play Store or Apple App Store by default (Apple’s TestFlight is invite-only). WhatsApp introduced Chat Lock a while ago, but version 3
Warning: Downloading APKs from random websites can lead to malware. Proceed with caution. Whatsapp Beta 3.3.10 Download