Information, news and technology group Reuters, will work with Symantec on the development of new security products, under a four-year alliance.
The deal, worth an estimated $3m (£2m), will make Reuters one of only a dozen large IT users around the world that feed into the design of Symantec's security software, through the supplier's customer advisory council.
The alliance, the first of its type for Reuters, marks a growing trend among corporate IT departments to forge closer relationships with a smaller number of suppliers.
"The programme means we will have good connections with Symantec as an organisation and a better working relationship. I can have more influence on the direction of their product and the way it works, and with other products that come out in the future," said Tim Voss, director at Reuters Global IT Security Risk Group.
Reuters believes this level of co-operation will give it a significant competitive advantage. The company is developing new security systems as it moves its proprietary information services to the Internet.
"Security is a differentiator for us. We can tell our customers that our systems are more secure and therefore more reliable. It means they can trust us more than their competitors," said Voss.
Reuters, which has central staff of 30 IT security specialists in addition to local specialists in its offices around the world, has traditionally developed its own security systems in-house.
But with a growing number of its services migrating to the Internet the group is beginning to incorporate more off-the-shelf software into its systems.
Under the deal, Reuters will use Symantec's Enterprise Security Manager package to automatically monitor the compliance of its IT systems and networks around the world with the group's security policies.
The package will inform central IT security staff of security risks, including known vulnerabilities in operating systems, details of users downloading or changing files, or anti-virus software that is incorrectly configured.
The package will use a database of Reuter's physical and intellectual assets to give an assessment of the level of risk posed by each breach of Reuter's IT security policy detected.
Symantec will also provide Reuters with a global incident response service, which will offer experts at short notice to assist with virus infections, hacking attempts or denial-of-service attacks.
Although it is using more off-the-shelf packages, the company plans to retain most of its security development in-house.
"Most commercial products protect you from kiddie scripts and disgruntled employees, but they don't necessarily protect you against groups with more resources," said Voss.
Reuters has developed its own systems to guard against threats from organised crime, and attempts at infiltration by well-resourced foreign governments, said Voss.