Most Internet users have been targeted at some point by hackers using malicious emails, the head of the Department of Homeland Security said Wednesday.

Speaking in the context of the breach at the Democratic National Committee, DHS Secretary Jeh Johnson told listeners that they should be aware of the fact they are being targeted, often by state-backed hackers. “Everybody in this room, I suspect, [through] your employer, has received an email that is an attempt at spearphishing. Simply by not opening the email or the attachment to the email that looks suspicious to you, or you don’t recognize, can make a huge difference.