You need to scan your computer thoroughly with a freshly updated virus scanner, and some antimalware software. Preferably two different virus scanners just to reduce the chances of something nasty slipping through the net.
As far as antimalware software goes, I recommend downloading hijackthis, malwarebytes and spybot seek and destroy. I can assist with going through the logfiles of hijackthis and spybot for you. Oh, and WARN YOUR CONTACTS! make sure they do not download any attachments they are not specifically expecting to come from you, and of the possibility of your computer being insecure.
All tho software I suggest is freeware, or a free version is available for DL in the case of malwarebytes. Hope this helps CBC.