Firms were warned by Inspector Norman Russell -- top ranking crime prevention officer with City police -- to be especially vigilant when taking on temporary staff in an interview with the London Evening Standard, published Monday.
Russell says: "We are advising these institutions to watch out for people taking jobs for a few weeks with the intention of infiltrating the systems and preparing them for hacking attack."
Companies have been told that those applying for temporary work are a particular threat and to carefully inspect employee references of in the run up to May 1.
Saboteurs could theoretically gain unauthorised access to computer networks and cause damage by placing a Trojan horse programs within a company firewall. They could also hide an application on the network timed to attack the computer system during May's demonstrations.
Take me to Hackers