Sergey Fionov
Leading Software Engineer at AdGuard
Cyprus
Summary
🤩
Rockstar🎓
Top SchoolSergey Fionov is a seasoned C++ team lead with 17 years of experience building low-level, cross-platform systems and networking infrastructure, currently leading the development of AdGuard’s system-wide filtering engine. His background spans system programming for hosting (Ceph, QEMU, kernel modules), BGP and Flowspec implementations, and software-defined storage, giving him deep expertise in performance-sensitive, security-oriented engineering. Comfortable across the stack, he has also delivered frontend and backend solutions earlier in his career and contributed to private cloud projects. Based in Cyprus and educated in applied mathematics and system programming at MSU, Sergey blends rigorous academic grounding with hands-on leadership in production-critical C++ systems. An under-the-radar strength is his long-term focus on networking and OS-level tooling, which informs pragmatic design choices for robust cross-platform products.
17 years of coding experience
5 years of employment as a software developer
Specialist, Applied Mathematics/Computer Science/System Programming, Specialist, Applied Mathematics/Computer Science/System Programming at Московский Государственный Университет им. М.В. Ломоносова (МГУ)
Английский, Русский
Github Skills (161)
bug-tracker10
websocket10
async10
ftp10
adblock10
blocking10
notification10
sdk10
android-application10
filtering10
ads10
ldap10
cross-platform10
dot10
advertising10
Programming languages (15)
Github contributions (5)
AdguardTeam/DnsLibs
Oct 2019 - Jan 2023
DNS filtering library
Contributions:14 releases, 206 commits, 11 pushes in 3 years 4 months
dns-filterdnsdns-over-httpsfilteringadguard
AdguardTeam/AdGuardVPNCLI
Apr 2024 - Mar 2025
Contributions:6 reviews, 5 PRs, 31 pushes in 1 year
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