Photos: Inside Sophos Labs

The outside of the Sophos building, designed by company's two chief executives, near Oxford. It's called 'The Pentagon' because of its security features. The moat around the outside is to stop ram raiders, while the car park contains wedges that can be raised to prevent a vehicle from leaving in the event of a physical attack.

For the full story on what goes on in The Pentagon, read our feature. 

The entrance hall leads to meeting rooms and the dining hall on the ground floor, which visitors do not need security clearance for. Visitors to the second and third floors (which include the antivirus labs) need clearance and must be accompanied by Sophos staff.

The secure area outside the antivirus labs. Devices with Internet access are barred from the labs, including Wi-Fi enabled laptops and 3G mobile phones. This is because they risk either infecting the closed networks within the labs, or being infected themselves by malicious code on the virus sample testing network.

Visitors must pass through two security gates to get to this point. There is still a third security gate restricting access to the labs. 

The antivirus labs uses heuristic algorithms and signature detection to analyse rogue code. The different systems for analysis and testing of malware samples are physically separate, to avoid one system infecting the other.

Thirty researchers use the labs to analyse spam and malware, working with a further 20 analysts globally. Malware is collected from honeypots and sent in by customers. Major threats are flashed up on overhead monitors.

The quality assurance labs "thrash antivirus software" 24/7 on a variety of different hardware and operating systems. Apple Mac, Unix, Linux and Windows systems are all tested.