Détection attaque spyware

Bonjour,

depuis ce matin, mon pc m'envoie des alertes.
"System Alert.
System has detected a number of active spyware applications that may impact the performance of your computer. Click the icon to get rid of unwanted spyware by downloading an up-to-date antispyware solution. "
ou
"System alert : Malware threats.
Your computer is infected with a back door Trojan that allows the remote attacker to perform various malicious actions. Click this baloon to download malware removal software."

Que dois je faire ???
Qui peut m'aider ?

Par avance merci de vos infos.

Lili