Tā yǐqián shì ge wǎngchóng, jīngcháng zài wǎngbā áoyè dǎ yóuxì.
He used to be an internet addict, often staying up all night in internet cafés playing games.
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网虫 was everyday slang in the internet-café era of the late 1990s and 2000s and now sounds a little dated. It is formed like 书虫 'bookworm'. The neutral word for the problem is 网瘾 'internet addiction'.
