It's looking like you got phished a long time ago, or installed malware which targeted the lastpass extension.
Did all of you use the same OS four years ago? (Windows perhaps?) Some malware targets Chrome/Firefox files on disk. A malicious extension probably wouldn't be able to affect your LastPass extension, but a malicious malware app could easily modify it.
It's looking like you got phished a long time ago, or installed malware which targeted the lastpass extension.
Did all of you use the same OS four years ago? (Windows perhaps?) Some malware targets Chrome/Firefox files on disk. A malicious extension probably wouldn't be able to affect your LastPass extension, but a malicious malware app could easily modify it.