On the afternoon of 24 February, a group of masked protesters gathered outside the home of a biologist from the University of California, Santa Cruz. According to police reports, insults were hurled at the family home, the front door was battered and the biologist's husband assaulted. Although the identities of the protesters are still unknown, the events bear the hallmarks of an attack by animal-rights activists. If this is true, it will be depressingly familiar. A few days earlier, for example, the University of California, Los Angeles, secured a restraining order against five activists who had been harassing a primate researcher (see Nature 451, 1041; 2008).

The tactics deployed by animal-rights extremists aim to intimidate researchers, and there are signs that these activists are becoming more brazen, willing to visit homes rather than just trash laboratories. “I can't imagine, if this continues, that it's not going to give researchers pause,” says Frankie Trull, president of advocacy organization the Foundation for Biomedical Research. But as yet there is no evidence of such a trend, although there has been a handful of high-profile cases in which researchers have changed their jobs after being threatened (see Nature 444, 808–810; 2006).

Violent protest and threats are no way to engage in debate and dialogue, and researchers who are involved in humane animal research should bind together as a community to ensure that the extremists' approach doesn't succeed. Working together, the research community can explain to the public the value of its work — as well as promptly communicating any hints of threats to colleagues and administrators. In the United States, researchers would also be wise to tell their deans if their data are requested under the Freedom of Information Act, as this can sometimes be a sign that activists are hunting for targets. And universities need to be proactive. They should identify those researchers who are potential targets and be prepared to offer them additional security. There should be no reason to adjust careers — although for some engaged in animal research, heightened awareness and additional protection may have to become part of the daily routine.