X0306 4 2019-08-14 0 0001580808 A10 Networks, Inc. ATEN 0001443284 Singer Eric C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001606750 VIEX Opportunities Fund, LP Series One C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001659404 VIEX Opportunities Fund, LP - Series Two C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001654852 VIEX GP, LLC C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001619127 VIEX Special Opportunities Fund II, LP C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001658891 VIEX Special Opportunities GP II, LLC C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001619126 VIEX Special Opportunities Fund III, LP C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001676049 VIEX Special Opportunities GP III, LLC C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 0001619125 VIEX Capital Advisors, LLC C/O A10 NETWORKS, INC. 3 WEST PLUMERIA DRIVE SAN JOSE CA 95134 1 0 0 0 Common Stock, par value $0.00001 2019-08-14 4 X 0 45200 7.50 A 3576422 I By Viex Special Opportunities Fund II, LP Common Stock, par value $0.00001 2019-08-15 4 X 0 217900 7.50 A 3794322 I By Viex Special Opportunities Fund II, LP Common Stock, par value $0.00001 30120 D Common Stock, par value $0.00001 1658360 I By Viex Opportunities Fund, LP - Series One Common Stock, par value $0.00001 331977 I By Viex Opportunities Fund, LP - Series Two Common Stock, par value $0.00001 271116 I By Viex Special Opportunities Fund III, LP Put Option (Obligation to Buy) 7.50 2019-08-14 4 X 0 452 0.00 D 2019-08-16 Common Stock, par value $0.00001 45200 13227 I By Viex Special Opportunities Fund II, LP Put Option (Obligation to Buy) 7.50 2019-08-15 4 X 0 2179 0.00 D 2019-08-16 Common Stock, par value $0.00001 217900 11048 I By Viex Special Opportunities Fund II, LP Call Option (Right to Buy) 2.50 2019-07-30 2019-11-15 Common Stock, par value $0.00001 150900 1509 I By Viex Opportunities Fund, LP - Series Two Call Option (Right to Buy) 2.50 2019-07-30 2019-11-15 Common Stock, par value $0.00001 150000 1500 I By Viex Special Opportunities Fund II, LP Call Option (Right to Buy) 5.00 2019-07-30 2019-11-15 Common Stock, par value $0.00001 5900 59 I By Viex Special Opportunities Fund II, LP Put Option (Obligation to Buy) 5.00 2019-07-30 2019-08-16 Common Stock, par value $0.00001 111700 1117 I By Viex Special Opportunities Fund II, LP Put Option (Obligation to Buy) 7.50 2019-07-30 2019-11-15 Common Stock, par value $0.00001 200000 2000 I By Viex Special Opportunities Fund II, LP Call Option (Right to Buy) 2.50 2019-07-30 2019-11-15 Common Stock, par value $0.00001 210500 2105 I By Viex Special Opportunities Fund III, LP Call Option (Right to Buy) 5.00 2019-07-30 2019-11-15 Common Stock, par value $0.00001 5800 58 I By Viex Special Opportunities Fund III, LP Shares of Common Stock of A10 Networks, Inc. (the "Issuer") beneficially owned directly by VSO II or options sold by VSO II. The transactions reported herein represent the exercises of (i) 452 put option contracts on August 14, 2019 and (ii) 2,179 put option contracts on August 15, 2019 sold by VSO II, each contract representing 100 shares of Issuer Common Stock, by the counterparty and the acquisition of the shares underlying such put options by VSO II. VSO GP II, as the general partner of VSO II, may be deemed the beneficial owner of the shares of Common Stock of the Issuer beneficially owned by VSO II. VIEX Capital, as the investment manager of VSO II, may be deemed the beneficial owner of the shares of Common Stock of the Issuer beneficially owned by VSO II. Mr. Singer, as the managing member of each of VSO GP II and VIEX Capital, may be deemed the beneficial owner of the shares of Common Stock of the Issuer beneficially owned by VSO II. This Form 4 is filed jointly by VIEX Opportunities Fund, LP - Series One ("Series One"), a series of VIEX Opportunities Fund, LP, VIEX Opportunities Fund, LP - Series Two ("Series Two"), a series of VIEX Opportunities Fund, LP, VIEX Special Opportunities Fund II, LP ("VSO II"), Viex Special Opportunities Fund III, LP ("VSO III"), VIEX GP, LLC ("VIEX GP"), VIEX Special Opportunities GP II, LLC ("VSO GP II"), Viex Special Opportunities GP III, LLC ("VSO GP III"), VIEX Capital Advisors, LLC ("VIEX Capital"), and Eric Singer (collectively, the "Reporting Persons"). Securities of the Issuer beneficially owned directly by VSO II. VSO GP II, as the general partner of VSO II, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by VSO II. VIEX Capital, as the investment manager of VSO II, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by VSO II. Mr. Singer, as the managing member of each of VSO GP II and VIEX Capital, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by VSO II. Each Reporting Person disclaims beneficial ownership of the securities of the Issuer reported herein except to the extent of his or its pecuniary interest therein, and this report shall not be deemed to be an admission that any Reporting Person is the beneficial owner of such securities for purposes of Section 16 or for any other purpose. Securities of A10 Networks, Inc. (the "Issuer") beneficially owned directly by Series One. VIEX GP, as the general partner of Series One, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by Series One. VIEX Capital, as the investment manager of Series One, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by Series One. Mr. Singer, as the managing member of each of VIEX GP and VIEX Capital, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by Series One. Securities of the Issuer beneficially owned directly by Series Two. VIEX GP, as the general partner of Series Two, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by Series Two. VIEX Capital, as the investment manager of Series Two, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by Series Two. Mr. Singer, as the managing member of each of VIEX GP and VIEX Capital, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by Series Two. Securities of the Issuer beneficially owned directly by VSO III. VSO GP III, as the general partner of VSO III, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by VSO III. VIEX Capital, as the investment manager of VSO III, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by VSO III. Mr. Singer, as the managing member of each of VSO GP III and VIEX Capital, may be deemed the beneficial owner of the securities of the Issuer beneficially owned by VSO III. These options are currently exercisable. /s/ Eric Singer 2019-08-16 VIEX OPPORTUNITIES FUND, LP - SERIES ONE By: VIEX GP, LLC, its General Partner, Name: /s/ Eric Singer, Title: Managing Partner 2019-08-16 VIEX OPPORTUNITIES FUND, LP - SERIES TWO By: VIEX GP, LLC, its General Partner, Name: /s/ Eric Singer, Title: Managing Partner 2019-08-16 VIEX GP, LLC, its General Partner, Name: /s/ Eric Singer, Title: Managing Partner 2019-08-16 VIEX SPECIAL OPPORTUNITIES FUND II, LP By: VIEX Special Opportunities GP II, LLC, its General Partner, Name: /s/ Eric Singer, Title: Managing Member 2019-08-16 VIEX SPECIAL OPPORTUNITIES GP II, LLC Name: /s/ Eric Singer, Title: Managing Member 2019-08-16 VIEX SPECIAL OPPORTUNITIES FUND III, LP By: VIEX Special Opportunities GP III, LLC, its General Partner, Name: /s/ Eric Singer, Title: Managing Member 2019-08-16 VIEX SPECIAL OPPORTUNITIES GP III, LLC Name: /s/ Eric Singer, Title: Managing Member 2019-08-16 VIEX CAPITAL ADVISORS, LLC, its General Partner, Name: /s/ Eric Singer, Title: Managing Partner 2019-08-16