If you use LINED internet connection (like the one provided by BSNL via Land line phone, broadband and dial-up). Then, don't use it during thundering and terrestrial lightening ('Bijli kadkna'). The lightening has the tendency to travel via phone line ( when earthing is not proper). This can destroy your modem, and even PC.

What to do: During lightening and thundering, completely disconnect your telephone cable from the telephone  connector box. If possible, switch off your PC as well.
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