Security issues after logging out !! please help

[pranav2794]

hi,
i observed in many of the highly secured websites like bank sites etc. that after logging out of the account, they show the message in the logout page "For security reasons : please close this webpage "
I was wondering what could have been the reason behind this. How one could hack into the account by taking advantage of this.

[LoGiCaL__]

After logging out of a site you may have some residual cookies still on your computer from your previous session on whatever website you were logged into. If you happened to just log out and go to a not so secure site it would be possible to retrieve that information.