Anti-spam firm ClearMyMail has claimed 100 per cent protection against PDF spam, as spammers change their tactics in a bid to flood mailboxes.

One of the latest techniques spammers are using to try and get through spam blockers is to attach a PDF file to their emails. This PDF file will then contain the spammers’ sales message, making it difficult for traditional spam blockers as most spam blockers are unable to read the contents.

ClearMyMail said the majority of these PDF spam emails are simple ‘Pump and Dump’ scams but blocking all emails with PDF files is not an option either, as this would end up losing legitimate emails.

The other problem is that a normal spam email will be roughly 4-8k in size but a PDF spam will often be 24k or more. PDF spam emails will quickly fill up a mailbox and then waste bandwidth and time by being downloaded.

Dan Field, managing director of ClearMyMail, said: "Because we are an online service we can react much faster than traditional desktop software spam filters.

"As soon as our engineers have identified a new type of spam we can instantly update our system for all our customers before any spam reaches them."