Thanks for further clarification. Verbal approvals are not good.
However, your reference to Spolsky is not correct as nginx was not a side project, but a core work project that powered all of Rambler's properties. The situation is similar to a Yahoo employee open-sourcing the Apache Traffic Server (very similar project with similar timelines, by the way; Rambler was once the "Russian Yahoo", while Yandex is the "Russian Google") and then Yahoo 10 years later claiming the open-sourcing was illegal. I understand that something may have been done wrong (and that's why I appreciate Eclipse and Apache legal team support and due diligence), but I have a hard time believing that Rambler didn't notice its core internal project being open-sourced for 10 years.
The subtle thing here is that in the US and the UK typically things created "in the course of employment" (as defined in UK) would typically be owned by the employer. This is enforced either through a contract (e.g., in US), or both national law by default and the contract (e.g., in UK). So the employee would have no right to just open source things, or even create a business around it later.
This is why a mentioned that Spolsky's article - it explains the reasoning behind this situation very well.
In Russia things are different. I don't really understand all the legal details. It all boils down to Sysoev's contract and his precise duties.
Anyways, Sysoev was an system admin at Rambler at the height of its popularity in early 00s. I believe that Rambler management back then did not really understand the importance of OSS, or even software in general, or search engine business in particular. This is not unsimilar to the Yahoo story.
So Rambler just ignored the whole thing back in the day. So did Sysoev - the public is not aware of any written permission he was given in regards to Nginx. This situation lacks the legal clarity necessary for a working businesses... Now that Nginx is bigger than Rambler ever was, scavengers decided to check if they can find a dollar or two here.
However, your reference to Spolsky is not correct as nginx was not a side project, but a core work project that powered all of Rambler's properties. The situation is similar to a Yahoo employee open-sourcing the Apache Traffic Server (very similar project with similar timelines, by the way; Rambler was once the "Russian Yahoo", while Yandex is the "Russian Google") and then Yahoo 10 years later claiming the open-sourcing was illegal. I understand that something may have been done wrong (and that's why I appreciate Eclipse and Apache legal team support and due diligence), but I have a hard time believing that Rambler didn't notice its core internal project being open-sourced for 10 years.