Half of the UK’s medium to large sized businesses are struggling to deal with image based spam, as the abundance of such emails grows by the day, according to new research.

It is now thought that messages containing images also represent up to half of all spam, with PDFs accounting for 6% to 8% of the problem.

Nearly all medium to large businesses in the UK have anti-spam solutions, according to a survey of 400 medium to large businesses by network and email security software vendor PineApp. But anti-spam technology often fails to tackle image based spam, which is difficult for systems to pick out.

The survey found that the worst problem associated with PDF spam is the size of the files, with typical messages three times the size of normal spam.

The research found 48% of respondents said image based spam was clogging up bandwidth, while 37% said the storage space it took up was a major concern.

Earlier this month, a huge spike in PDF spam was reported with the messages representing over a tenth of spam on one day.