MI5 is the agency responsible for national security (as opposed to spooks in the MI6 foreign intelligence service, who are involved in covert operations abroad).
A section of the site goes into detail about the types of electronic attack that UK businesses face and advises firms to do a risk assessment of who might target them. It also warns of the "insider threat" from a firm's own staff.
"Electronic attack may come from a range of sources - criminals, foreign intelligence services, terrorists or lone hackers," the site says.
A brief guide to threats from hacking, malicious software, malicious modifications to hardware that permit an attack to be launched and denial of service are outlined. The information is pretty basic for any dedicated IT security officer but there are links through to more comprehensive government business continuity and emergency planning websites.
Of more interest to most people will be the section of the site aimed at dispelling "myths" about the UK's secret service. One such myth is that MI5 assassinates troublesome people. "It is claimed from time to time that we have been responsible for murdering individuals who have become "inconvenient" in some way. We do not kill people or arrange their assassination," the site states, in a matter of fact tone.
Wannabe spooks over 6ft will also be relieved to note: "Contrary to media reporting, we do not just recruit people under 5ft 11. There is a height restriction in place for our mobile surveillance recruitment campaign, but no such restrictions exist for any of the other campaigns. You can be tall and work for the Security Service!"
Home Secretary David Blunkett said in a statement: "The risk from terrorism is very real and we have a duty to ensure that individuals and businesses are armed with the information that allows them to take sensible and proportionate steps to protect themselves from new and emerging threats."