I would seriously advise you use a firewall it is dangerous to be online without one, as it could be that your computer has been infected or is under attack.
My personal advice is run adaware se 1.06 then spybot 1.4 and some Microsoft Antispyware, then download Sygate Personal Firewall and Avast! Home all of which are available with
www.google.com
This could be a attack or problem with any spyware/malware/virus/ internet related attack.