Two days before the first Large Hadron Collider experiment, one of the websites dedicated to the controversial project was defaced by hackers who identified themselves as the GST, or Greek Security Team.

The U.K. newspaper, The Telegraph, reported today that  the hackers temporarily replaced a message on one of the European Organization for Nuclear Research’s or CERN sites with a message reading “We are 2600—don’t mess with us.”

James Gilles, a spokesperson for CERN told the Telegraph that the project’s network was not permanently damaged.

“It was defacement, and that’s all it was,” said Gilles. “It was benign, but it reminds us that we need to be vigilant.”

The site has since been brought back up but is now available only to CERN users.