This problem affects the following MacBooks:
MacBook (13-inch, Late 2007)
MacBook (13-inch, Early 2008)
MacBook (13-inch, Late 2008)
MacBook Pro (15-inch, Early 2008)
MacBook Pro (17-inch, Early 2008)
MacBook Pro (17-inch, Late 2008)
Symptoms include ping dropping to 200-2000ms, network speeds dropping to 1-5Mbps, slow browsing, slow downloads.
Luckily, there’s a fix for that:
Link to the fix.
