Symantec moved a step closer to joining the ranks of the leading broad-based corporate software sellers on Thursday as it announced a $12.5bn all-stock agreement to buy storage and data back-up company Veritas.

However, the move by the fast-growing security software company hit its shares hard this week. On Thursday, Symantec's stock had fallen 23 per cent, or about $5bn, since news of the impending deal emerged.