Happened to me, no idea what the suspicious activity was, I imagined sending spam emails or something, seems their security ain't that great as I have heard quite a few people had to do this to get access back.
I had it a few months ago and binned the whole bloody lot.
Never used it since then.
I used my gmail account for Worldpay payments so didn't want to take any chances. I got done by Paypal once and it caused hassle for months swapping bank accounts,didn't want to go down that route again.