Holding(s) in Company

TR-1: NOTIFICATION OF MAJOR INTEREST IN SHARESi

1. Identity of the issuer or the underlying issuerof existing shares to which voting rights areattached: ii

Corero Network Security plc

2 Reason for the notification (please tick the appropriate box or boxes):

An acquisition or disposal of voting rights

x

An acquisition or disposal of qualifying financial instruments which may result in the acquisition of shares already issued to which voting rights are attached

An acquisition or disposal of instruments with similar economic effect to qualifying financial instruments

An event changing the breakdown of voting rights

Other (please specify):

Dilution due to the issuance of new shares under a placing, subscription and open offer

3. Full name of person(s) subject to thenotification obligation: iii

Peter Kennedy Gain

4. Full name of shareholder(s)  (if different from 3.):iv

Peter Kennedy Gain

Draper Gain Investments Limited

(a company wholly owned by Peter Kennedy Gain)

5. Date of the transaction and date onwhich the threshold is crossed orreached: v

5 April 2017

6. Date on which issuer notified:

7 April 2017

7. Threshold(s) that is/are crossed orreached: vi, vii

7%

8. Notified details:

A: Voting rights attached to shares viii, ix

Class/type ofshares

if possible usingthe ISIN CODE

Situation previousto the triggeringtransaction

Resulting situation after the triggering transaction

NumberofShares

NumberofVotingRights

Numberof shares

Number of votingrights

% of voting rights x

Direct

Direct xi

Indirect xii

Direct

Indirect

GB00B54X0432

10,733,333

10,733,333

9,533,333

9,533,333

4,900,000

4.7%

2.4%

B: Qualifying Financial Instruments

Resulting situation after the triggering transaction

Type of financialinstrument

Expirationdate xiii

Exercise/Conversion Period xiv

Number of votingrights that may beacquired if theinstrument isexercised/ converted.

% of votingrights

C: Financial Instruments with similar economic effect to Qualifying Financial Instruments xv, xvi

Resulting situation after the triggering transaction

Type of financialinstrument

Exercise price

Expiration date xvii

Exercise/Conversion period xviii

Number of voting rights instrument refers to

% of voting rights xix, xx

Nominal

Delta

Total (A+B+C)

Number of voting rights

Percentage of voting rights

14,433,333

7.1%

9. Chain of controlled undertakings through which the voting rights and/or thefinancial instruments are effectively held, if applicable: xxi

Peter Kennedy Gain personally holds 9,533,3333 shares and 4,900,000 shares are held by Draper Gain Investments Ltd (a company wholly owned by Peter Kennedy Gain), total beneficial holding 7.1%.

Proxy Voting:

10. Name of the proxy holder:

11. Number of voting rights proxy holder will cease to hold:

12. Date on which proxy holder will cease to hold voting rights:

13. Additional information:

14. Contact name:

Peter Kennedy Gain

15. Contact telephone number: