O GuestBook está recebendo menssagens automaticas! Vírus?...

[Daniel.Filho]

Olá pessoal, estou com um problema no GuestBook do meu site joomla, sou leigo no assunto!
tenho mais de 90 menssagens que entram todo o dia do tipo:
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Os nomes que registraram são os mais variados, porém o endereço e sempre de New York
Isso deve ser algum tipo de vírus? O que faço para parar de receber este tipo de menssagem?
Desde já muito obrigado!