RSA was hired last week following a three-stage pitch against incumbent agency Harvard PR and two other agencies. Fees are understood to be in the region of £100,000.
RSA will focus on promoting Symantec's products to the business, IT trade and broadcast media.
Symantec's UK in-house comms team, based in Maidenhead, will continue to promote the firm's market-leading range of Norton software for consumers and small firms.
The RSA account team is led by senior consultant Mandy Hassall, who reports to Symantec senior PR manager for northern Europe Lucy Millington.
Hassall said: 'Internet security is a hot topic for both trade and business media. We want to take the subject beyond viruses and start to focus on it in a wider business context.'
RSA's targeting of the business media reflects Symantec's aim to increase the revenue it derives from corporate clients, from 60 per cent of total revenue to more than 70 per cent.
California-headquartered Symantec was founded in 1982 and operates in 38 countries. It has more than 4,000 staff worldwide.