WordPress users website targeted by hackers.

The botnet targets WordPress users with the username “admin”, trying thousands of possible passwords.

The attack began a week after WordPress beefed up its security with an optional two-step authentication log-in option.

The site currently powers 64m websites read by 371m people each month.

According to survey website W3Techs, around 17% of the world’s websites are powered by WordPress.

“Here’s what I would recommend: If you still use ‘admin’ as a username on your blog, change it, use a strong password,” wrote WordPress founder Matt Mullenweg on his blog.

He also advised adopting two-step authentication, which involves a personalised “secret number” allocated to users in addition to a username and password, and ensuring that the latest version of WordPress is installed.

“Most other advice isn’t great – supposedly this botnet has more than 90,000 IP addresses, so an IP-limiting or login-throttling plugin isn’t going to be great (they could try from a different IP [address] a second for 24 hours),” Mr Mullenweg added.

Matthew Prince, Chief Executive and co-founder of Cloudflare, said that the aim of the attack may have been to build a stronger botnet.

“One of the concerns of an attack like this is that the attacker is using a relatively weak botnet of home PCs in order to build a much larger botnet of beefy servers in preparation for a future attack,” he wrote in a blog post.

“These larger machines can cause much more damage in DDoS [Distributed Denial of Service] attacks because the servers have large network connections and are capable of generating significant amounts of traffic,” he added.

Hi-tech crime terms

• Bot – one of the individual computers in a botnet; bots are also called drones or zombies
• Botnet – a network of hijacked home computers, typically controlled by a criminal gang
• Malware – an abbreviation for malicious software ie a virus, trojan or worm that infects a PC
• DDoS (Distributed Denial of Service) – an attack that knocks out a computer by overwhelming it with data; thousands of PCs can take part, hence the “distributed”
• Drive-by download – a virus or trojan that starts to install as soon as a user visits a particular website
• IP address – the numerical identifier every machine connected to the net needs to ensure data goes to the right place