1krBlocker keeps a threat database on your phone: lists of websites known to steal data or spread harmful apps, and numbers known to send scams, collected from public sources such as CERT Polska. It's checked offline, for every message.
On the Why? screen, the Threat lists group shows matches:
- "Links to a known dangerous site (…, source: …)": the link's website is on a list. Don't open it; the link preview warns you strongly too.
- "Sender is on a known scam list (…, source: …)": the sending number is known for scams.
The source tells you which list it came from.
Keeping the lists fresh: they update automatically. To see when, open Settings → Threat database; Update now updates them now. Downloading lists sends nothing about you.
Your own rules show in the Your rules group: "Matches your rule “…”". If a rule catches messages it shouldn't, edit or turn it off in Settings → Rules.
Optionally, links can also be checked online with Google Safe Browsing (see "Checking links online").