I had a neighbor who called me over to his house after a storm. Most everything on his network was burned up.
We spent time diagnosing what worked and what did not. As time went on it was more and more obious that the Cable modem passed the lightning strike from the cable on the street to his entire network, burning up a multi-function printer, switches, wireless router, etc. Even some TVs in his home had burned up. Luckily that did not include the big flat screen in the Living room.
There were many UPSs, and Surge suppressors of many good brands instaled throughout. Also remember though, a surge supressor is only as good as he ground it is connected to. If you have no "real" grounded plugs like 3 prong plugs on old 2 conductor wiring, a surge supressor does NOTHING.
He had so innocently connected the devices one by one and assumed that all would be fine His Internet came from a cable provider that did not properly ground the cable line. This also meant that he often had "hum bars" on some analog channels only on his main TV. This was due to the lack of proper ground on the cable and small voltages travelling though his TV to the 3 prong plug ground. This can also affect digital channels but is less obvious what the cause is.
Then came the lightning strike!
1) In North America there is a requirement to ground the Cable at the point of entry to the home. You can use a Splitter, tap or Grounding block. It does not matter, as long as it is grounded. You will need n further grounding on the cable line and in fact is probably undesirable. Once you do this there is no need to ground each splitter as another poster here claims. That ground is carried on the shield of the coax to any device connected to the coax. This will theoretically pass the lightning strike from the any part of the coaxial line to ground.
2) In North America it is also mandatorry that a copper phone line have a Lightning supressor that is grounded. This theoretically will pass a lightning strike to the phone / DSL line to the ground.
3) Electrical grounds are also used for a device with a three prong plug.
4) Quality of grounds is also an issue. There are some that will tell you that grounding to a cold water pipe is an acceptable method when in fact it is NOT. A good ground is 8 feet long . wiring directly to the shield of a coax (by way of grounding block) or a Lightning supressor on copper Phone/DSL line. https://www.wikihow.com/Install-Ground-Rods. Most DSL or Cable providers will not install a proper ground rod. It is common to often see these services fgrounded incorrectly to a cold water pipe. They get away with it because it is 'Low voltage" but that does not take into account a lightning strike.
5) Quantity of grounds is also an issue. It is even possible to have multiple grounds cause problems such as "hum bars" in analog TVs, or just digital breakup due to small voltages travelling from one ground potential to another along a coax line because it is grounded at multiple ponts each ground with its own ground potential. The greater the differences in Ground potential the more obvious these hum bars may be. The length and qulity of ground wire also affects ground potential. Also, although you may not see hum bars in a digital signal, the ACRipple or hum can still interfere. This may also be called "Ground Loops" . Most any technician who has dealt with analog audio or video can tell you about ground loops. Digital is not completely immune.
6) a lightning strike (or any electricity) will always take the path of least resistance to ground
Let us assume that lightning strikes a pole or line outside your home and there is no (or a poor quality) protection or grounding at the point of entry to the home. The strike will pass along to your modem to any device with a grounded connector and probably fry anything between your modem and the first "good" ground it finds. The strike will take the path of least resistance (or multiple paths) to the ground so if the "best" ground is by way of a 3 prong plug on your TV that lightning spike will be carried mostly through your TV to ground, probably frying your TV along the way.
Now with a proper , high quality ground at the point of entry , if there is a lightning strike to pole or line outside, that lightning should dischage to ground BEFORE entering the home. THIS IS THE REASON WHY YOU DO NOT SIMPLY GROUND TO A COLD WATER PIPE!
As general rule (and may also apply to most any device that connects to a wire that passes outside):
1) Ground ALL Cable, Phone and DSL copper lines at point of entry
2) If your modem connects to a router or switch with a grounded outlet make sure it is grounded or provide a separate ground . Some switches and network hardware have a grounding screw . If you have a lot of network hardware at that point, such as in a rack, it is best to ground ALL of it at that point to an ISOLATED ground, not the electrical ground and defeating any electrical grounds in favour of an isolated ground. Some might in turn connect the Isolated ground in placeof the electrical ground (third prong)
3) ground any Satellite, TV, FM or other antenna at the point it enters the home. DO NOT attach coax to antenna masts, it should use some standoffs to help insulate it from the mast like these
https://www.amazon.com/Antenna-Standoff-Outdoor-Off-Air-Attachment/dp/B00UU39QKM , otherwise the Mast is like a lightning rod with a wire connecting to the inside of your home, or Deloran.
Of course none of this will help much if the lightning comes in the window and strikes a TV or computer directly.
Have you ever noticed that in a hospital the outlets are red/orange and often marked "Isolated Ground" ? You would not want a lightning strike to find its way to a half-baked electrical ground only to later find a new path to a better ground by way of YOUR BODY while you are connected to a piece of medical equipment .