Kolkata: In one of the biggest cyber attacks reported in recent times, Pakistani hackers have defaced and mutilated over 800 Indian government and corporate websites on the eve of India's Independence Day.

The risk in the cross-border hacking activity, which increases manifold just before August 15 and the Republic Day every year, was especially high this time with some critical system 'bugs' being reported in the past two weeks, a computer network security group said on August 14.

BFI Secure, the cyber security wing of BFI Groups, formed by former and present students of the computer science and engineering department of the Indian Institute of Technology, Kharagpur, on August 14 said the Indian websites hacked included government as well as corporate sites.

Among the major government sites hacked were NFR.ernet.gov.in, Hyderabadwater.gov.in, ER.railnet.gov.in and Panjabseva.gov.in, founder of the BFI Groups Bikash Barai said.

The Army of six cyber experts, who have been keeping constant vigil on the internet, said the major Pakistani group behind the stepped up hacking was the Federal Bureau of Hacking (FBH) followed by BugsPakistan, Powhat and Switchex.

"While Pakistani cyber criminals have hacked over 757 sites from January to July this year, in August alone they destroyed over 1000 Indian sites," Darai said.

PTI