In a public report Wednesday, researchers at security company FireEye Inc said the group used the unusual tandem as a means of communicating with previously infected computers. FireEye has briefed law enforcement on what it found.

The technique, uncovered during a FireEye investigation at an unnamed victim organization, shows how government-backed hackers can shift tactics on the fly after they are discovered.

"It's striking how many layers of obfuscation that the group adopts," said FireEye Strategic Analysis Manager Jennifer Weedon. "These groups are innovating and becoming more creative."

The machines were given an algorithm for checking a different Twitter account every day. If a human agent registered that account and tweeted a certain message, instructions for a series of actions by the computer would be activated.