"What's the matter, scared?" ~ Scarecrow Shrieker
The Scarecrow Gang are an enemy faction found in DC Universe Online and, as their name suggest, are avid followers of the supervillain Scarecrow - they are mostly active in Gotham City and are one of the first enemy factions heroes loyal to the DC villains and one of many enemies Batman will encounter.
The Scarecrow Gang are described in-game by Oracle as being just as crazy as Scarecrow is and although Batman doesn't quite give them that much credit he does realize the threat they pose and has heroes take out the gang's attempts to panic all of Gotham using Fear Gas.
The Scarecrow Gang are so fanatically devoted to Scarecrow that they even go as far as attacking officers and doctors trying to aid stricken citizens and administer cures for the Fear Gas - which again puts them in conflict with young heroes.
Although hostile towards heroes the Scarecrow Gang do not seem to be hostile towards villains, presumably due to the fact villains would not be too concerned with stopping the gang's mayhem (especially since most villains in Gotham are mentored by the Joker - who is notorious for his insanity).