In the last couple of days, my MBP stopped running anything, because no application could open a file; all file handles in the OS were used! Using the unix lsof command, I discovered that a process named "cookied" was consuming all of the files. Here is a small portion of the output: cookied 2597 caff 48u PSXSHM 4096 e.Safari.PrivateBrowsing-10068 cookied 2597 caff 49u PSXSHM 4096 e.Safari.PrivateBrowsing-10069 cookied 2597 caff 50u PSXSHM 4096 e.Safari.PrivateBrowsing-10070 cookied 2597 caff 51u PSXSHM 4096 e.Safari.PrivateBrowsing-10071 cookied 2597 caff 52u PSXSHM 4096 e.Safari.PrivateBrowsing-10072 cookied 2597 caff 53u PSXSHM 4096 e.Safari.PrivateBrowsing-10073 cookied 2597 caff 54u PSXSHM 4096 e.Safari.PrivateBrowsing-10074 cookied 2597 caff 55u PSXSHM 4096 e.Safari.PrivateBrowsing-10075 cookied 2597 caff 56u PSXSHM 4096 e.Safari.PrivateBrowsing-10076 cookied 2597 caff 57u PSXSHM 4096 apple.Safari.PrivateBrowsing-0 cookied 2597 caff 58u PSXSHM 4096 FNetwork.defaultStorageSession cookied 2597 caff 59u PSXSHM 4096 apple.Safari.PrivateBrowsing-2 cookied 2597 caff 60u PSXSHM 4096 e.Safari.PrivateBrowsing-10077 So, the "cookied" process has opened over 10,000 "files". I killed the process, which releases all of those file handles. But if Safari is running, the same process comes right back and starts opening files. If I quit Safari, and then kill the cookied process, it does not come back (unless I start Safari, again). Note also that Safari is not running in Private Browsing mode (despite the name of the files). In fact, Private Browsing has not been enabled for at least a couple weeks. Running Chrome does not cause the problem. This could be a bug in Safari, or it could be a virus which is triggered only when running Safari. No Google search I could come up with provides any clues.