One in 78 links sent via instant messaging (IM) programs is to malicious content, according to security company MessageLabs.

The company said this was an increase of 78 per cent over the past six months.

Paul Wood, intelligence senior analyst at MessageLabs said the increase in threats was down to hackers breaking through Captcha technology.

This technology, which involves the user having to read a distorted image of a word and enter that text correctly, is often used when people register for an IM account.

“Bypassing Captcha technology enables the bad guys to create large numbers of fake but valid online accounts", said Mr Wood. "

These are used by spammers to send malicious links via IM that redirect victims to spam websites and sometimes compromised websites.”

The report also found that levels of spam, or junk email, were unchanged since May, remaining at 90.4 per cent. The company said this was largely due to the several hours during which Cutwail, one of the largest and most active botnets, was inoperative following the shutdown of California-based internet service provider, Pricewert LLC on 5 June.