I assume that your contract states that without any notice the lease agreement would be automaticaly prolonged for 30 days. This mean that in case the lease terminated on July 1, 2005 and there is no notice in place on June 1, 2005 - the lease is assumed by both parties as in effect till August 1, 2005. And so on.
Thus, moving out without any notice would be a violation of the contract. It doesn't mean however that you forfait your security deposit. You need to look what the contract is saying this matter - in which situation the security deposit could be taken.
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