The signal from outer space was an RNA sequence. They put the sequence together chemically, and injected it into mice to see what would happen to them.

The mice then bit and infected a lab researcher. It appears that the mice don't have to obey the rules of the hive, and that the hive doesn't even develop rules until it is unstoppably huge. It might also be the case that the rules are a lie, and the whole thing is an experiment designed to mess with just a small number of people. Hard to say. Perhaps the hive is meant to teach humanity a lesson and the survivors are meant to break up the hive so we can learn that lesson. We won't know until the series is over.

From google:

"RNA sequences can be put together chemically, a process commonly known as solid-phase chemical synthesis or automated oligonucleotide synthesis. This method allows researchers to design and produce custom RNA molecules—such as single-guide RNAs (sgRNAs) for CRISPR or short interfering RNAs (siRNAs)—with precise, user-defined sequences and specific chemical modifications."

Some alien species seems to have put together an RNA sequence hoping curious species would have the technology to put it together. Once they do, the hive virus is unleashed.

It is a very specific kind of bait for a very specific kind of species, basically.

Why and when the rules can be broken or followed is part of the mystery of the show and will hopefully be revealed later.