Universities are target of hundreds of bomb hoaxes Clare College at Cambridge University, one of the many targets of the hoax emails. Photograph: geogphotos/Alamy Universities across the country are being terrorised by what detectives believe is a linked series of bomb threats designed to cause chaos on campuses. Around 50 institutions have been the victim of hundreds of hoaxes in the past month, forcing the evacuation of buildings and prompting an urgent escalation in security. Scotland Yard's counter-terrorism branch, SO15, has launched a national investigation into the threats plaguing some of the country's most high-profile institutions. Some threats have been made over the phone, but the majority are being sent to the universities through an anonymous remailer, a server that receives messages with embedded instructions on where to send them next, and forwards them without revealing where they originally came from. Cambridge University has received daily warnings over the last three weeks of incendiary devices planted on its estate, forcing the evacuation of buildings, including 14th-century Clare College, whose alumni include the broadcaster and naturalist Sir David Attenborough. A spokesman for the university said: "It has been three weeks now that we have been seeing overnight emails at a specific address at the university, alleging that there are incendiary devices or other such at various locations. They have been daily. No devices have been found at all, but we do treat each message seriously and inform the police and the relevant authorities. In some cases we have needed to evacuate, in others just carry out security sweeps. Detectives have been left mystified as to what might be the motive behind the threats, which often mention specific buildings and at other times warn generally of a bomb "somewhere on campus." An emailed hoax to halls of residence at Bristol University in April, which forced evacuations, said: "Two small bombs are hidden in Wills and Durdham Halls. They will explode later today. Take this warning very, very seriously. David Alder, director of communications and marketing for the university, said its students and staff had been "calm" each time, but concerns were growing. He said: "We have had a dozen or so threats since the first one on the 23 April. They have all been hoaxes, but we have had to take them all seriously. The first one we received was specific to two halls of residence, but the majority have been fairly random. Our security team is working with other universities. We are treating each one as if it is the first. There appears to be no link between the universities that have been targeted, which include Essex and Durham universities, University College London and the University of the West of England. A Scotland Yard spokesman said: "This is being treated as a suspected linked series of malicious communications. These threats have the potential to cause distress and disruption.