New Delhi, May 27 (PTI): Computer security analysts have issued an alert for Internet users and operators against hackers attempting to target websites of ''reputed'' government and private organisations.

Cyber security agencies have also asked Internet users to deploy adequate firewalls and security measures to combat these attacks originating through Distributed Denial of Service (DDoS).

"It is observed that some hacker groups are launching distributed denial of service attacks on websites of government and private organisations in India. The attacks may be targeted to different websites of reputed organisations.

"These attacks are being launched through popular DDoS tools and can consume bandwidth requiring appropriate proactive actions in coordination with service providers," Indian Computer Emergency Response Team (CERT-In), the country's national agency to respond to computer security incidents, said in its latest advisory.

A DDoS attack can be understood as one in which a host of compromised systems attack a single target resulting in denial of service for users of the targeted system. A stream of messages subsequently sent to the target system then forces it to shut down thereby denying service to legitimate users.

The agency along with security analysts in the private domain have also recommended a host of pro-active measures to ensure users are safe against these hacking attempts.

"Deploy appropriate intrusion or DDoS prevention system capable of detecting and mitigating DDoS attacks and ensure that intrusion system contains signatures to detect the attacks launched from common DDoS tools, among others," the agency said.

"Such attack can be prevented provided the specialised cyber security tools are activated and updated regularly," a security analyst said.Indicating an increasing trend in security incidents in the country's cyberspace, the government had recently, during the just concluded session of the Parliament, said that the CERT-In has handled over 13,000 such incidents in 2011 as compared to 8,266 incidents in 2009.

"CERT-In has observed that there is significant increase in the number of cyber security incidents in the country. A total of 8,266, 10,315 and 13,301 security incidents were reported to and handled by CERT-In during 2009, 2010 and 2011, respectively," Minister of State for Communications and IT Sachin Pilot had said in a written reply to Rajya Sabha.

These security incidents include website intrusions, phishing, network probing, spread of malicious code like virus, worms and spam, he had said.

The agency has also asked the operators to report to it such instances at -- incident@cert-in.org.in.