Another gotcha with offsite backups

Back in February I wrote about a potential problem with offsite backups, that if you delete a file by accident, many providers will delete their copy of the file too, leaving you with no backup. Recently, Mathew Ingram of Gigaom described another potential problem with off-site backups, one most likely to affect Windows users.

His ISP, Rogers Communications in Canada, has a monthly bandwidth cap of 95 gigabytes. He had been over the cap before, so when he was alerted by Rogers about being over again, he thought nothing of it.

But, a Rogers an online tool that shows daily usage, reported that his household had used more than 100 GB in less than 2 days. Yikes. 

His first suspect was an unprotected WiFi network, but that wasn't the source of the problem.

The other people in his house all claimed to be innocent of huge downloads. But, someone in his house had been using a file sharing network so, at first, Ingram was confident that was the problem

But no.

Then, he writes "I checked every computer in the house to make sure there were no programs running in the background or viruses or malware". There weren't. 

The bandwidth hog wasn't obvious until he got his monthly bill from Amazon AWS. His normal bill for storing 25GB was $3, the latest bill was $109. And, he writes, "... the amount of data that Amazon says I consumed in April (a little over 600 gigabytes) is almost exactly the same as the amount of extra bandwidth that my ISP says I used in the month...".

So, why was a computer in his house re-downloading all of his backed up files, time and time again? 

To virus scan them. 

He uses Jungle Disk, which maps the Amazon file storage to a Windows drive letter. A Jungle Disk note from 2009 warns: 

It is important to understand that when using some anti-virus software, you will want to make sure the Jungle Disk network drive is excluded from your list of scanned drives. When a virus scanner checks files on a network drive, it must download the file and look in the contents for signs of infection and as such, can result in increased download bandwidth. 

Another possible suspect is desktop search software such as the Windows search indexing service. 

Just something to be aware of when mapping off-site backups to Windows drive letters. 

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