The top 10 most significant cybersecurity incidents globally this year (2021) are:

1. SolarWinds Supply Chain Attack: This cyberattack compromised multiple organizations worldwide, including government agencies and leading technology companies.

2. Microsoft Exchange Server Vulnerabilities: A series of zero-day vulnerabilities in Microsoft Exchange Servers led to widespread hacking and data breaches across numerous organizations.

3. Colonial Pipeline Ransomware Attack: One of the largest cyber attacks on critical infrastructure, this ransomware attack disrupted fuel supplies across the eastern United States.

4. Accellion Data Breach: Cybercriminals exploited vulnerabilities in Accellion’s File Transfer Appliance (FTA), resulting in data breaches affecting multiple high-profile organizations.

5. JBS Cyber Attack: The world’s largest meat processing company, JBS, experienced a ransomware attack, leading to temporary shutdowns and affecting the global meat supply chain.

6. Kaseya Ransomware Attack: Ransomware gang REvil targeted the software provider Kaseya, exploiting its remote management software to compromise hundreds of businesses worldwide.

7. LinkedIn Data Leak: The personal data of 700 million LinkedIn users was scraped and put up for sale on a hacker forum, potentially exposing users to identity theft and phishing attempts.

8. T-Mobile Data Breach: T-Mobile, a major US telecom provider, experienced a data breach that exposed personal information of over 50 million customers.

9. PrintNightmare Vulnerability: A critical vulnerability in Windows Print Spooler, known as “PrintNightmare,” allowed attackers to execute arbitrary code remotely, potentially impacting millions of systems.

10. Pegasus Spyware Revelations: The Pegasus spyware, developed by NSO Group, was used for targeted surveillance, infecting the mobile devices of journalists, activists, and political figures worldwide.

Please note that this list is not exhaustive, and there have been numerous other significant cybersecurity incidents this year.