Social networking website Meetup.com is fighting a sustained battle against cyber attackers who are demanding only $300 to call off a campaign that has kept the site offline for much of the past four days.

The site, which enables strangers to meet for activities of shared interest such as sports and other hobbies, could not be accessed early Monday afternoon.

A Meetup blog said that the company was a victim of a distributed denial of service (DDOS) campaign, a type of attack that knocks websites offline by overwhelming them with incoming traffic. It said that no personal data, including credit card information, had been accessed.

(Read more: Record-breaking DDoS attack strikes CloudFlare's network)

Meetup's co-founder and CEO, Scott Heiferman, said on the company's blog that it was the first such attack in the site's 12-year history. He defended themove not to pay the paltry ransom.

"We made a decision not to negotiate with criminals,'' he said. "Payment could make us (and all well-meaning organizations like us) a target for further extortion demands as word spread in the criminal world.''