A message on the site says it has been compromised by a security exploit
High-profile technology blog TechCrunch has been taken offline by hackers.
A message on the site said that it had been "compromised by a security exploit" but did not specify any further details.
"We're working to identify the exploit and will bring the site back online shortly," the message read.
The site went down at around 0620 GMT and was replaced by various messages including a link to a site directing people towards adult material.
The site has come back online at various times since it was first hacked, but has not yet stabilised.
Graham Cluley of security firm Sophos said in a blog post: "There's no such time as a 'good time' to be hacked of course, but one can only imagine that today is a better day for TechCrunch to be hacked than tomorrow when the site will, presumably, be expecting a large amount of traffic."
Apple is expected to make an announcement about a new product on Wednesday - possibly a tablet computer - which TechCrunch will closely follow.
"This hack is a salutary warning to all website owners that everyone has to be on their guard against hacking, whether your site is big or small," said Mr Cluley.
TechCrunch was founded by entrepreneur Michael Arrington and profiles Silicon Valley start-ups and technology firms across the US.
It is regarded as one of the most influential technology sites on the internet.