What causes someone's claim of PIP or ADP to be investigated?

[butterfluff]

So to be clear, I'm not on PIP etc and I am not claiming it. Anyone I know who does get it seems to be to be entirely entitled to whatever help they can get.

I do see reports online though about people being investigated and sometimes in the news of people being caught out.

What I am curious about is what leads to these investigations in the first place?
Is it generally just someone they know reporting them or do other things flag it up?

The largest percentage is being reported by someone..... then it can be Checks against tax records or other databases reveal discrepancies... etc..

Thanks. I suppose people should probably just keep their status as being in receipt of benefits to themselves. I thought your income didn't matter for PIP for example although I can see how tax records would show if you were claiming other benefits fraudulently.