However, said the company, the websites are now working normally, and business is unlikely to be affected.
The suspected hardware failure took place on Tuesday evening.
The websites impacted were the real estate classifieds firm 99acres.com, matromonial site jeevansathi.com, job postings website naukrigulf.com and education-focused shiksha.com.
“The reason for such outage of the aforesaid websites seems to be hardware failure at the third party data centre where our servers are co-located.
“We are investigating the matter to find out the exact & detailed reasons for this outage,” it said, adding that it didn’t expect any “any material impact on the overall business of the company” from the downtime.
The company did not specify how long the websites were down.