It is possible that lightning strike can seriously damage or entirely destroy a computer. It doesn't even need to strike directly outside your house, it can strike miles away and still be dangerous. I worked in a computer service. A client brought a computer after a storm with lighting strikes. The computer wasn't even powered ON during the storm but was connected to electricity. It was totaly destroyed, TOTALY. I know it happens very rare but it happens so I suggest to unplug a computer from electricity, any routers and wifi cable if you have a wifi antenna on the roof. It takes only a second to do, but can save your computer.

The surge protection units that sit at the wall to your house are entirely optional AND expensive (as in, your expense). At a guess you'd maybe find 2 out of 100 homes that have them around here. It's not just lightning, any surge on the grid can blow out everything in your home. A truck hit a pole here a few years back and the resulting surge blew out literally everything in all the houses near it.

A surge of that size will simply jump any in home surge protection you might have, those units are not rated for that many joules. That size of a surge will fry everything, no in home stuff will help unless you have data center quality units.

My dad used to do it too. :D
I have connected my computer with a socketbox which has surgeprotection, still I have to keep my fingers crossed to see if it works in case of a lighningstrike.

Over 10 years ago I witnessed the aftermath of a lightningstrike in the town where my sister lives. It struck a house and blew a huge hole in the roof (1 yard/meter approx). Very strong stuff indeed that atmospheric electricity.

You misunderstood, it's essentially an urban legend that lightning strikes can enter the home via a telephone line or cable connection. There's supposed to be grounding specifically because of that. What's more, it's unusual to even have a surge protector which even provides protection for the cable. You'd think those would be a lot more common if there was any point.

The information in it in general isn't terribly reliable and mostly consists of rumor, but unless the lightening strike is fairly close to the home, this shouldn't be a problem for the equipment and the further away you are from the strike the less energy there is to damage equipment and the more effective the grounding is. But, it doesn't look like something that's received much research.

The reason to unplug is that storms move and sometimes rapidly and a strike to a nearby pole would vaporize all sorts of stuff. But, you'd almost certainly notice a lightning strike outside.

EDIT: move this one down.
As for lightning strikes miles away. I'm going to have to call BS on that, perhaps you have poorly engineered electrical equipment in Poland, but there's no way that it would travel through that many transformers to damage units miles away. Every block or so it travels you have 4 blocks worth of extra wire to dissipate into and by the time you get to a mile out you're talking about a huge number of homes that would be affected.

Very much possible. Not just with computers. My dad would get called out many a night to go fix two-way radio stations that got hit. Even with all the grounding and surge protection that's on those, they still get blown out.

About two years ago there was a lightning strike so close to our apartment it made my wife and I both temporarily deaf. I didn't even know it was lightning because I was away from all the windows. I just felt things shake and then the smoke detectors beeping kind of faded into hearing. I was just getting ready to unplug the computers, but just wasn't fast enough. Luckily it only killed the onboard ethernet stuff and after installing a card, was back up and running.
I think most I've bought have had either cable or phone protection, or both. The UPS I have on this has both. I'd have to check the surge protector I have on other items, it might just have phone, but I know it has one or the other.

Not refuting what you said in general (I don't know myself), but I think their more common than you think.

When I was bothering with that, I had to search to find them and most stores didn't have them at all. That may have changed more recently, but I had very few options when I wanted to do that and for things like the cable box it's not even supported due to signal degredation.

Of course a close lightening strike is a completely different matter as you get things like damage from the EMP blast as well as enough current to induce current on the other side of the grounding. Not to mention that if it manages to get into the house the pulse is fast enough to blow through surge protectors without getting any benefit.

That being said, there really isn't a lot of good information out there as far as I can tell. Best things seems to be to just unplug everything as that's pretty much the only way to be safe.

It's a good idea as you're not going to be protected from surges by lightning coming in via the power wires.

I mostly started posting because people blame the telephone and cable connections when those are generally exit points for the electricity. The power lines are much larger coming into the house and are also generally the ones that are at the top of the telephone poles. So, they're the ones that get hit and they're the ones that bring in damn near all the surge to the house.

The gauge of the wires just dictates that the ones used for delivering electricity are going to conduct a hell of a lot more before they fry. Any reports to the contrary should be taken with a grain of salt.

I took a lightning zap myself, through a computer. I had a steel-framed Northgate Omnikey hooked up to my rig and was playing something, dunno what. Thunderstorm rolled in quickly and a bolt struck somewhere awfully darn close. Felt a jolt a bit heavier than a 110 VAC line, but it lasted just a split second so it was more of a surprise than anything else. Computer didn't miss a beat. I think I was using just a cheapo power strip with wink-wink-nudge-nudge surge suppression on it. You know, the little breaker that never pops. And it didn't pop.

Seen power variations cause quite a few problems on machinery. One component in particular was sensitive to incoming power fluctuation, and the machine manufacturer didn't put any protection on it. A few times customers called to say this particular servo drive "exploded". "What do you mean, 'exploded'?" "I mean it blew the fuck up!" One of our salesmen went over to one of these customers after it happened, to see if there was anything he could do. He asked the same thing - what do mean by 'exploded'? The operator told him the interface panel just blew right off the front of the unit. The salesman looked at the servo drive and commented that it looked fine, since the panel was on the drive. The operator told him to stand back and watch, flipped on the main power, and the panel flew about 15 feet out of the cabinet with a loud bang, passing right between the two of them. "Yeah, I guess it explodes." "Wanna see it again?"

Stupid OEM was too cheap to buy the inexpensive line reactors that the drive manufacturer recommended so we warrantied an assload of those things. Eventually the drive manufacturer noticed that we were sending in a large number of drives for repair, and then told us what was going on.

And this is why, boys and girls, computer build threads always have multiple people recommending that one should not go cheap on the power supply: a good PSU can shrug off a lot of that garbage coming down the line.

My dad had a phone switch, ADSL modem, and a couple computers damaged by lightning. They had been thorough and pulled all computer stuff from the mains, the trouble was just: the surge came from the phone line. With the phone line gone, the burglar alarm went haywire and started screaming. The whole family was on vacation, so it took a while to get the thing to shut up.

The network stuff was damaged, but on the computers, only the NICs didn't work despite them being integrated to the motherboard (bought new NICs, computers worked fine).

I once got zapped through the mouse during a thunderstorm. It burned like crazy and my muscles spasmed so much that I couldn't voluntarily move my fingers for many minutes (all in all, it was very unpleasant). It took almost half an hour before I fully regained the ability to move my fingers properly again. Funnily enough, the laptop still works, but the battery won't hold a charge (and the OS gives a "the battery may be damaged" popup at startup). It was the first lightning of the storm, took me completely by surprise, and I think it hit close because everything turned white for what was probably just a flash but felt like a few seconds and the noise was out of this world (or maybe my brain got fried).

Nowadays I instinctively jump away from the computer the moment I see or hear lightning.

Anyway, I think it's better to unplug everything during a thunderstorm. On top of it sounding pretty legit on its own, a computer repair guy I know said that it's really important.

During thunderstorms and power outages I switch off the circuit breakers for all the electrical outlets in the house leaving on only those for the lights. The phone/VDSL line is protected trough an UPS also serving the modem and the router. And I'm not living in an area known for frequent surges or power outages, It's just good practice.

Some years ago when I was in a small house in the mountains, during a thunderstorm the charger from the video camera was fried while being plugged in. I remember seeing a blue light coming out of the electrical outlet. So these things happen. It is just that some areas are more at risk than others.

A Lightning fried my network card once. But only because it was connected directly via cable that was in the ground -> lightning voltage came through cable directly.

In other case it's not possible, since everything goes through fuses -> they fry first and then disable the power.

Fuses only protect from over currents (or short circuits). Surge protection devices protect you from over voltages and these are not fitted as standard in household installations.

Remember that most surge protectors aren't rated for lightning. I unplug all my electrics when there's a thunderstorm on and use my netbook or read a book. It's better to be safe than sorry and I live atop a hill with no tree cover around so I'm at the highest point... there's a house on a hill directly opposite me too at the same level that has a flag pole & I've watched seen that get struck.