When you think of subs you may think of Subway or "The Hunt for Red October," but right now we're talking about subtitle files, which are downloaded for pirated movies. Hackers have found a way to make those text files malicious.
Internet security expert Robert Siciliano says this is new.
"It's interesting; we've never seen something like this in the wild with subtitle code."
Stephen Coty is chief security evangelist at Houston’s Alert Logic.
"When it's scrolling and the VLC player is launching those subtitles, it's actually running background processes on your machine."
Right now antivirus programs don't scan for this and Siciliano says about the only hope is that your media player, like VLC, will patch its software.
"The companies, such as VLC and others that provide players are already issuing patches."
Coty says this will be a difficult attack to track.
"Well, right now it's pretty undetectable because it only functions when you're watching or streaming."
So make sure your media player is up to date -- or, of course, you could just not download pirated movies.