On my very first game, only a few days ago, I encountered this hack for the first time, and only just now, after having seen it quite a few more times, I've figured out that it must be a hack.
Basically what happened is somehow someone built at least 30 alien eggs around the alien base - with a significant amount of defense, too. Recently, I've seen cases where you walk into a human base on ATCS only to be zapped by one of 20 tesla coils at the entrance. In another case, I was unable to build anything, so I decided to remove one of perhaps 15 sentry guns. After removing about 5 of them I was still unable to build, due to power over-consumption.
How the heck do they do this? I'll take a screenshot next time it happens.
Has anyone else encountered this?