To check your browser extensions for malware, open your browser's extensions page (chrome://extensions in Chrome, edge://extensions in Edge, about:addons in Firefox, or Safari > Settings > Extensions on a Mac). Remove anything you don't recognise or no longer use. For each extension you keep, open Details and check its permissions, its site access and where it came from. Watch for extensions marked "Installed by your administrator" on a personal computer, or ones that come back after you remove them. Those usually mean other software on the PC is installing them, so run a malware scan next.

Browser extensions are brilliant. I use a password manager, an ad blocker and a couple of developer tools every day. But an extension sits right inside your browser, and depending on its permissions it can see every page you visit, including your email and online banking.

Most extensions are honest.…