The browser extension was hijacked on Google Web Store. That update included alert10.js, malware that opens popups saying you have a virus.
Vulnerable component: Chrometana (Chrome extension)
CVSSv3 score: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H/E:H/RL:O/RC:C
CWE-ID: CWE-798 - Use of Hard-coded Credentials
The vulnerability allows a remote attacker to gain unauthorized access to victim's browser.
The vulnerability exists due to presence of backdoor code in Chrometana Google Chrome extension 1.1.3, distributed via Google Web Store.
Known APT campaigns:
Attack against Google Web Store developer accounts
Accounts of several developers of Google Chrome extensions were compromised. The malicious actors published new version of Chrome extension, which contained backdoor code. The campaign has started approximately in March 2017 and continued in August 2017. The total verified number of compromised extensions equals 6. Approximate number of affected victims - 4.1 million, according to Proofpoint.