Ruby on Rails No route matches [GET] "/manager/html" -

i see error many times in ruby on rails log file. don´t know come from?

f, [2015-07-13t13:03:00.178740 #22638] fatal -- : actioncontroller::routingerror (no route matches [get] "/manager/html"):   actionpack (4.0.0) lib/action_dispatch/middleware/debug_exceptions.rb:21:in `call'   actionpack (4.0.0) lib/action_dispatch/middleware/show_exceptions.rb:30:in `call'   railties (4.0.0) lib/rails/rack/logger.rb:38:in `call_app'   railties (4.0.0) lib/rails/rack/logger.rb:21:in `block in call'   activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `block in tagged'   activesupport (4.0.0) lib/active_support/tagged_logging.rb:25:in `tagged'   activesupport (4.0.0) lib/active_support/tagged_logging.rb:67:in `tagged'   railties (4.0.0) lib/rails/rack/logger.rb:21:in `call'   actionpack (4.0.0) lib/action_dispatch/middleware/request_id.rb:21:in `call'   rack (1.5.2) lib/rack/methodoverride.rb:21:in `call'   rack (1.5.2) lib/rack/runtime.rb:17:in `call'   activesupport (4.0.0) lib/active_support/cache/strategy/local_cache.rb:83:in `call'   railties (4.0.0) lib/rails/engine.rb:511:in `call'   railties (4.0.0) lib/rails/application.rb:97:in `call'   puma (2.10.1) lib/puma/configuration.rb:74:in `call'   puma (2.10.1) lib/puma/server.rb:490:in `handle_request'   puma (2.10.1) lib/puma/server.rb:361:in `process_client'   puma (2.10.1) lib/puma/server.rb:254:in `block in run'   puma (2.10.1) lib/puma/thread_pool.rb:96:in `call'   puma (2.10.1) lib/puma/thread_pool.rb:96:in `block in spawn_thread' 

these errors represent lame attempts hackers exploit various known vulnerabilities in other applications.

see more details here.