EMC is to buy RSA Security for around $2.1bn (£1.2bn) so it can offer its storage customers new encryption and other security products.
RSA had been seeking a buyer and EMC said it moved fast to stop a rival snapping up the security company.
EMC has annual sales of around $10bn and RSA around $300m, although RSA’s industry profile is very high and it is seen as a leader in business security offerings.
RSA has 1,200 employees and is based near EMC’s US headquarters. The plan is to allow RSA to operate as a free-standing unit as EMC’s information security division.
EMC said it expected to complete the acquisition in the third or fourth quarter. RSA is EMC's most expensive takeover to date; others include Dantz, Documentum, Legato, Rainfinity, Captiva and VMware.