Not wishing to scare you too much

but think of it this way:-
What information does your bank ask to identify yourself online or over the phone? Probably 2 or 3 of the following:-
- Account No
- Password
- Address
- Date of Birth
- Place of Birth
- Mothers Maiden Name
If you're putting details of your relatives on a genealogy website you will probably be supplying the last 3 of those. Address can usually be found via Electoral Roll lookups (opting out of it doesn't hide your details from the commercial verison of the roll which can be accessed online). All that a bunch of criminals need to do is get your account No & password, which they can do by phishing scams and the like and, hey presto, they have total access to your relatives accounts! That
will be a nice surprise for them

Another nightmare story to think about is that some paedophile rings apparently harvest pictures of children from websites for dubious purposes. Do you really want photos of your nephews/nieces/cousins in the hands of these guys?

Companies like to encourage us to put our information on their sites as the more info they have the more marketable they are but what is really in it for us? Of course they will say they will keep the info safe but if people like Gary McKinnon can hack repeatedly into heavily resourced US Military and NASA computers, and the British Government departments have a habit of leaking information, what chance is there that small companies can realistically protect themselves from hacker gangs? Virtually none..
I don't mean to give you nightmares but we really need to weigh up what we are gaining from giving websites this valuable information and what we can lose from it..