Hi,
I had this issue before as well, the solution to the problem is as follows:
1. Run a virus scan on your machine, make sure you have the latest virus updates, if you want a free one try AVG Free, or if you have money then try Kaspersky, Nod32, McAfree or Norton these all have free trials as well if you dont want to buy.
2. Run a scan with a spyware program such as Adware or Windows Defender
3. Change your hotmail password, check out this site from microsoft https://www.microsoft.com/protect/fraud/passwords/checker.aspx which will tell you what is considered to be a secure password.
Good luck
Hope that helps
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In response to UK_PC_Technician post:
Mcafee or Norton, are not useless and are used by several global companies around the world, if you are going to dismiss both these products then you need to back it up with some facts.
Please dont take information from people who are not qualified IT specialists, especially when it comes to your security.
I am an IT specialist as I am a Developer in a large organisation, my specific role may not be security but I know enough to cover the average home user, the information I provided the user is sufficent with there problem.