Here is an article which is a couple of years old but may help.
http://news.bbc.co.uk/1/hi/technology/3528810. stm
The two most important things you can do are:
INSTALL A FIREWALL (if not done so already)
INSTALL ANTI-VIRUS (if not done so already)
There are free versions of good firewall and antiivirus so if you dont have either let us know via this question and we will give you some advice on what products to use.
If you HAVE got a firewall and anti-virus then maybe you need to run a spyware checker, and again there are good free versions around. Ask for advice here.