The owner of property website Zoopla and comparison site Uswitch is to be bought by a US private equity firm.
Silver Lake is paying £2.2bn for ZPG, which also owns the PrimeLocation and SmartNewHomes websites.
Investors in ZPG will receive 490p a share - almost a third higher than its closing price on Thursday.
"ZPG is a great growth technology company," said Silver Lake managing director Simon Patterson.
"It has established strong positions in property classifieds, home and financial services markets by innovating in product and marketing."
ZPG founder and chief executive Alex Chesterman said: "Silver Lake is the global leader in technology investing and I am firmly of the belief that ZPG will benefit from their technology expertise and global network which will help accelerate our growth."
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