Cloud Computing provides many types of services mainly SaaS, PaaS, IaaS. Each of them has its own security challenges, but IaaS undertakes all types of challenges viz., network attack and request based attacks ie handling the requests from untrusted users, XSS (cross-site scripting attack), DDOS and many more. These attacks are independent of each other and consequently the QoS provided by cloud is compromised. This paper proposes a Behaviour based IDS (Intrusion Detection System) BIDS. BIDS provides detection of untrusted users, false requests that may lead to spoofing, XSS or DOS attack and many such possible attacks. In addition, there are certain cases where user login or password is compromised. BIDs can be helpful in detecting such attacks and maintaining the QoS of cloud.