By default, it's on and keeps restore points up to one month I think.
And its NOT REVERSABLE.
No it doesn't forget up and no it doesn't ALWAYS work.
The most you could lose is a couple files.
Check the latest restore point and back up anything after that time.
Also, make sure you revert to a point before the virus.
EDIT: First though get a screenshot of the security balloon and tell us your operating system.