Spyware alert

Bonjour,
Comment se débarrasser de messages indiquant que mon ordinateur est infecté par un spyware, qui apparaissent à intervalles réguliers, et qui me proposent d'acheter un Anti-Spyware (à tarif réduit...) ?
Voici les deux messages qui alternent:

Spyware alert ! Vulnerabilities found Your computer is infected by spyware. 25 serious threats are found while scanning your files and registry. It is strongly recommended to entirely clean your computer and activate the on-fly protection against future intrusions. Why you need to be protected against spyware ?
! Upgrade to full version of WinSpyware Protect security kit to clean your computer and prevent new security and privacy attacks. You will have daily updates and online protection against Internet attacks
Activate WinSpyware Protect (ou bien) Stay unprotected

2e message:
WinSpyware Protect alert
Infiltration Alert
Your computer is being attacked from Internet. It could be a password-stealing attack, a trojan - dropper and so on
Details:
Attacks from (ici des numéros variables)
port (numéro variable)
Attacked port: (numéro variable)
Threat: (info variable)
Do you want WinSpyware Protect to block this attack ?
Yes No

Merci de m'aider