I've had items mysteriously disappear, and I've later logged in and found them.
Most recently, it was an extra princess dress during Halloween month.
The shoes were still there, but the rest of the dress parts weren't.
I checked again a few days later, and the dress parts were there again.
However, there are other items that have gone forever, and I don't know
what happened. I chalk it up to a VMK game bug.
The only way someone could have gotten your stuff is if you use a browser
that lets you save passwords automatically for logging in, and someone else
has access to your computer. Or if someone knows your log in name and
password, then they have access easily.
I don't believe there's a random hacker out there.
I will keep an eye out for it in case it decids to return home 
