Whirlpool Washing Machine leaking water?

On returning to my Washing machine to do more washing after a week or so, i found that the drum had water in it, and it smelt really bad.

I've been told that it could be the filter, and so when i hada look, loads of water came out of that.

Also been told that it could be the water coming back into the machine after been taken out. Therefore will been a washer to prevent the water from getting back in.

Is that right?

Any help would be very much appreicated.

Danni