There are two types of users a fake comment can come from: A bot, and a paid basher. Both will usually only post during market hours (4am EST to 8pm EST). Bots usually post in conjunction with a short attack. So when the stock is red, the bots come out.

What are paid bashers?

"Bashers" are posters who are notably and consistently negative on a stock. ... This poster claims he/she was paid $18 per hour, plus "$1.25 bonus for every decent quality post over 100 per day as well as a monthly bonus of $100 for every penny the stock had dropped from the previous month."

What are pumpers in stocks?

In a pump and dump scheme, fraudsters typically spread false or misleading information to create a buying frenzy that will “pump” up the price of a stock and then “dump” shares of the stock by selling their own shares at the inflated price.